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Definitions

• the invention generally concerns lead-free lithium doped potassium sodium niobate piezoelectric particles that have a single crystalline phase.
• a two-staged calcination processes for making these single crystalline phase particles is also disclosed.
• Piezoelectric materials are used in several components of medical diagnostic tools, industrial automation processes, and defense and communication systems. Such materials also find use in emerging fields such as micromotors, energy harvesting devices, magneto electric sensors and high power transformers.
• Piezoelectrical properties can be found in several types of materials and engineered ceramics.
• PZT lead zirconate titanate
• PbO lead oxide
• the presence of large amounts of lead (60 wt. % of lead oxide (PbO)) in PZT materials has, however, led to much attention during the past decade due to environmental concerns as well as governmental regulations against hazardous substances such as lead.
• Extensive research has since been conducted on the development of lead-free piezoelectric materials with high piezoelectric coefficient and electromechanical coupling factor.
• Ki -x Na x Nb0 3 KNN
• Na 0 .o5Bio .5 Ti0 3 BNT
• BaTi0 3 BaTi0 3
• Li doped KNN (K,Na) x Lii -x Nb03 (hereafter referred as, LiKNN) ceramics have shown a significant improvement in properties (d 33 -235 pC/N) at the phase boundary of orthogonal and tetragonal crystal structures within the range of 0.05 ⁇ x ⁇ 0.07.
• these bi- phasic LiKNN crystalline ceramics have not performed in a comparable manner with PZT- based ceramics.
• the solution resides in the production of a lead-free lithium doped potassium sodium niobate piezoelectric powder that has a single crystalline phase with well-defined particle size and morphology.
• at least one or both of these features contribute to the ceramic' s improved piezoelectric properties and allows the ceramic to be a commercially viable alternative to PZT-based ceramics.
• These structural features can be obtained by using a two-stage calcination process. It is believed that the first stage forms the single phase crystal structure such that secondary crystalline phases are not present. The second stage, which has a lower temperature and longer processing time than the first stage, contributes to the particle size and morphology of the ceramic powder of the present invention.
• a lead-free lithium doped potassium sodium niobate piezoelectric ceramic material in powdered form and having a single crystalline phase can have a formula of (K,N) x Lii -x Nb0 3 , In particularly preferred instances, x can be 0.05 ⁇ x ⁇ 0.07.
• the powdered single crystalline phase ceramic material can have a substantially cubical particle morphology.
• the cubical particle morphology can be a uniaxial cubical particle morphology.
• the ceramic material can be characterized by a powder x-ray diffraction pattern as substantially depicted in FIG. 4 (see 1000 (3H)-950(10h).
• the ceramic material can have a particle size distribution of 1.5 to 2, of 9 to 10.
• the ceramic material can have been calcined at a first temperature of 975 °C to 1050 °C for 2 to 4 hours and at a second temperature of 875 °C to less than 975 °C for 8 to 12 hours.
• the ceramic material can be calcined at a first temperature of about 1000 °C for about 3 hours and at a second temperature of about 900 to 950 °C, preferably about 950 °C, for about 10 hours.
• the ceramic material can have a perovskite structure.
• a lead-free piezoelectric composite material comprising: (a) any one of the lead-free lithium doped potassium sodium niobate piezoelectric ceramic materials of the present invention; and (b) a polymeric matrix, wherein the ceramic material is dispersed in the polymeric matrix.
• the composite material includes 5% to 50%, by volume, of the ceramic material.
• the polymeric matrix can be a thermoset polymeric matrix.
• thermoset polymeric matrices include those comprising an epoxy resin, an unsaturated polyester resin, a polyurethane, bakelite, duroplast, urea-formaldehyde, diallyl-phthalate, an epoxy vinylester, a polyimide, a cyanate ester of polycyanurate, dicyclopentadiene, a phenolic, a benzoxazine, co-polymers thereof, or blends thereof.
• the thermoset polymeric matrix is an epoxy resin.
• the epoxy resin can include diglycidyl ether bisphenol-A and polyoxypropylene diamine.
• the polymeric matrix can be a thermoplastic polymeric matrix.
• thermoplastic polymeric matrices include those that include polyethylene terephthalate (PET), a polycarbonate (PC) family of polymers, polybutylene terephthalate (PBT), poly(l,4-cyclohexylidene cyclohexane-l,4-dicarboxylate) (PCCD), glycol modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and their derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomers, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PS
• the thermoplastic polymeric matrix can include polypropylene, polyethylene, polyamide, a polycarbonate (PC) family of polymers, co-polymers thereof, or blends thereof.
• the lead- free piezoelectric composite material of the present invention can include (i) a piezoelectric charge constant (d 33 (pC/N)) of 10 to 14, preferably about 12; (ii) a dielectric constant ( ⁇ 33 (-) ) of 13 to 17, preferable about 15; and/or (iii) a piezoelectric voltage constant (g 33 (mV.m/N)) of 90 to 110, preferably about 95 to 100, or more preferably about 98.
• the composite material can be shaped into any type of form or mold. In one instance, for example, the material can be in the form of a film or sheet.
• the composite material can be structured as a 0-3 composite or as a 1-3 composite.
• the method can include: (a) obtaining a lead-free lithium doped potassium sodium niobate piezoelectric precursor material; and (b) subjecting the precursor material to a calcination procedure comprising: (i) a first calcination step that can include calcining the precursor material at a temperature of 975 °C to 1050 °C for 2 to 4 hours to obtain a first calcined material; and (ii) a second calcination step that can include calcining the first calcined material from step (i) at a temperature of 875 °C to less than 975 °C for 8 to 12 hours to obtain the lead-free lithium doped potassium sodium niobate piezoelectric ceramic material.
• the precursor material can include, consist essentially of, or consist of a mixture of K 2 C0 3 powder, Na 2 C0 3 powder, Li 2 C0 3 powder, and Nb 2 0 5 powder.
• the first calcination step can include calcining the precursor material at a temperature of about 1000 °C for about 3 hours to obtain the first calcined material and the second calcination step can include calcining the first calcined material from at a temperature of 900 °C to 950 °C, preferably about 950 °C, for about 10 hours.
• the process can include cooling the first calcined material to room temperature prior to performing the second calcination step.
• the cooled first calcined material can be milled prior to, or during, the second calcination step. After the second calcination step, the material can be cooled to room temperature.
• the produced lead-free lithium doped potassium sodium niobate piezoelectric ceramic material can be subjected to a sonification step.
• the first calcination step can be used to form the single crystalline phase.
• the second calcination step can be used to form the cubicle particle morphology.
• Embodiment 1 describes a lead-free lithium doped potassium sodium niobate piezoelectric ceramic material in powdered form and having a single crystalline phase.
• Embodiment 2 is the ceramic material of embodiment 1, having a following formula of (K,N) x Lii -x Nb0 3 , wherein x is 0.05 ⁇ x ⁇ 0.07.
• Embodiment 3 is the ceramic material of embodiment 2, wherein the powdered single crystalline phase ceramic material has a substantially cubical particle morphology.
• Embodiment 4 is the ceramic material of embodiment 3, wherein the cubical particle morphology is a uniaxial cubical particle morphology.
• Embodiment 5 is the ceramic material of any one of embodiments 1 to 4, having a particle size distribution of 1.5 to 2, of 9 to 10.
• Embodiment 6 is the ceramic material any one of embodiments 1 to 5, further characterized by a powder x-ray diffraction pattern as substantially depicted in FIG.
• Embodiment 7 is the ceramic material of any one of embodiments 1 to 6, wherein the material has been calcined at a first temperature of 975 °C to 1050 °C for 2 to 4 hours and at a second temperature of 875 °C to less than 975 °C for 8 to 12 hours.
• Embodiment 8 is the ceramic material of embodiment 7, wherein the material has been calcined at a first temperature of about 1000 °C for about 3 hours and at a second temperature of about 900 to 950 °C, preferably about 950 °C, for about 10 hours.
• Embodiment 9 is the ceramic material of any one of embodiments 1 to 8, wherein the ceramic material has a perovskite structure.
• Embodiment 10 is a lead-free piezoelectric composite material that includes (a) any one of the lead-free lithium doped potassium sodium niobate piezoelectric ceramic materials of embodiments 1 to 8; and (b) a polymeric matrix, wherein the ceramic material is dispersed in the polymeric matrix.
• Embodiment 11 is the lead-free piezoelectric composite material of embodiment 10, that includes 5% to 50%, by volume, of the ceramic material.
• Embodiment 12 is the lead-free piezoelectric composite material of any one of embodiments 10 to 11, wherein the polymeric matrix is a thermoset polymeric matrix.
• Embodiment 13 is the lead-free piezoelectric composite material of embodiment 12, wherein the thermoset polymeric matrix comprises an epoxy resin, an unsaturated polyester resin, a polyurethane, bakelite, duroplast, urea-formaldehyde, diallyl-phthalate, an epoxy vinylester, a polyimide, a cyanate ester of polycyanurate, dicyclopentadiene, a phenolic, a benzoxazine, co-polymers thereof, or blends thereof.
• Embodiment 14 is the lead-free piezoelectric composite material of embodiment 13, wherein the thermoset polymeric matrix is an epoxy resin.
• Embodiment 15 is the lead-free piezoelectric composite material of embodiment 14, wherein the epoxy resin comprises diglycidyl ether bisphenol-A and polyoxypropylene diamine.
• Embodiment 16 is the lead-free piezoelectric composite material of any one of embodiments 10 to 11, wherein the polymeric matrix is a thermoplastic polymeric matrix.
• Embodiment 17 is the lead-free piezoelectric composite material of embodiment 16, wherein the thermoplastic polymeric matrix comprises polyethylene terephthalate (PET), a polycarbonate (PC) family of polymers, polybutylene terephthalate (PBT), poly(l,4-cyclohexylidene cyclohexane-1,4- dicarboxylate) (PCCD), glycol modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and their derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomers, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polys
• Embodiment 18 is the lead-free piezoelectric composite material of embodiment 17, wherein the thermoplastic polymeric matrix comprises polypropylene, polyethylene, polyamide, a polycarbonate (PC) family of polymers, co-polymers thereof, or blends thereof.
• the thermoplastic polymeric matrix comprises polypropylene, polyethylene, polyamide, a polycarbonate (PC) family of polymers, co-polymers thereof, or blends thereof.
• Embodiment 19 is the lead-free piezoelectric composite material of embodiment 18, wherein the composite material has: (i) a piezoelectric charge constant (d 33 (pC/N)) of 10 to 14, preferably about 12; (ii) a dielectric constant ( ⁇ 33 (-) ) of 13 to 17, preferable about 15; and/or (iii) a piezoelectric voltage constant (g 33 (mV.m/N)) of 90 to 110, preferably about 95 to 100, or more preferably about 98.
• Embodiment 20 is the lead-free piezoelectric composite material of any one of embodiments 10 to 19, wherein the composite material is in the form of a film or sheet.
• Embodiment 21 is the lead-free piezoelectric composite materials of any one of embodiments 10 to 20, wherein the composite is a 0-3 composite.
• Embodiment 22 is the lead-free piezoelectric composite materials of any one of embodiments 10 to 21, wherein the composite is a 1-3 composite.
• Embodiment 23 is a method of making any one of the lead-free lithium doped potassium sodium niobate piezoelectric ceramic materials of embodiments 1 to 9, the method including (a) obtaining a lead-free lithium doped potassium sodium niobate piezoelectric precursor material; and (b) subjecting the precursor material to a calcination procedure that includes (i) a first calcination step that includes calcining the precursor material at a temperature of 975 °C to 1050 °C for 2 to 4 hours to obtain a first calcined material; and (ii) a second calcination step that includes calcining the first calcined material from step (i) at a temperature of 875 °C to less than 975 °C for 8 to 12 hours to obtain the lead-free lithium doped potassium sodium niobate piezoelectric ceramic material.
• Embodiment 24 is the method of embodiment 23, wherein the precursor material comprises a mixture of K 2 C0 3 powder, Na 2 C0 3 powder, Li 2 C0 3 powder, and Nb 2 0 5 powder.
• Embodiment 25 is the method of embodiment 24, wherein the first calcination step includes calcining the precursor material at a temperature of about 1000 °C for about 3 hours to obtain the first calcined material.
• Embodiment 26 is the method of embodiment 25, wherein the second calcination step includes calcining the first calcined material from step (i) at a temperature of 900 °C to 950 °C, preferably about 950 °C, for about 10 hours.
• Embodiment 27 is the method of any one of embodiments 23 to 26, further comprising cooling the first calcined material from step (i) to room temperature prior to performing the second calcination step.
• Embodiment 28 is the method of embodiment 27, that further includes milling the cooled first calcined material.
• Embodiment 29 is the method of any one of embodiments 26 to 27, further comprising cooling the obtained lead-free lithium doped potassium sodium niobate piezoelectric ceramic material from step (ii) to room temperature.
• Embodiment 30 is the method of any one of embodiments 23 to 29, wherein the obtained lead-free lithium doped potassium sodium niobate piezoelectric ceramic material is subjected to a sonification step.
• Embodiment 31 is the method of any one of embodiments 23 to 30, wherein the first calcined material from step (i) has a single crystalline phase.
• Embodiment 32 is a piezoelectric that inlcudes any one of the lead-free lithium doped potassium sodium niobate piezoelectric ceramic materials of embodiments 1 to 10 or the lead-free piezoelectric composite materials of embodiments 10 to 22.
• the piezoelectric device of claim 32 wherein the device is a piezoelectric sensor, a piezoelectric transducer, or a piezoelectric actuator.
• piezoelectric device comprising any one of the lead-free lithium doped potassium sodium niobate piezoelectric ceramic materials of the present invention or any one of the lead-free piezoelectric composite materials of the present invention, or both.
• piezoelectric devices include piezoelectric sensors, piezoelectric transducers, and piezoelectric actuators.
• composite refers to a material that includes two or more components mixed or dispersed together.
• piezoelectric includes a material that is capable of generating a voltage when a mechanical stress or vibration is applied to the material.
• a polymerizable matrix refers to a composition comprising monomers, polymers (two or more repeating structural units) or mixtures of monomers and polymers, or copolymers that can form a homogeneous or heterogeneous bulk composition when polymerized.
• wt.% or “vol.%” refers to a weight or volume percentage of a component based on the total weight or volume of material that includes the component. In a non-limiting example, 10 mL of a substance in 100 grams of the material is 10 vol.% of metal.
• the ceramic materials of the present invention can "comprise,” “consist essentially of,” or “consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase “consisting essentially of,” in one non-limiting aspect, a basic and novel characteristic of the ceramic materials of the present invention are their single crystalline phase structure and/or particle size and morphology.
• FIG. 1 is a flow chart of a method to make the ceramic piezoelectric ceramic materials.
• FIG. 2A is a schematic of a 0-3 piezoelectric ceramic composite.
• FIG. 2B is a schematic of a 1-3 piezoelectric ceramic composite.
• FIG. 3 is a graph of the two-stage calcination process of the present invention.
• FIG. 4 are XRD patterns of (K,Na) x Lii -x Nb03 powders after calcination under various conditions.
• FIG. 5 are graphs of particle size in micrometers versus volume percent for (K,Na) x Lii. x Nb0 3 powders after calcination under various conditions.
• FIG. 6A-E are SEM micrographs of (K,Na) x Lii -x Nb0 3 powders after calcination under various conditions.
• FIG. 7 A is a SEM tomography image DEP aligned KNN-epoxy composite of the present invention.
• FIG. 7B is an SEM image DEP aligned KNN-epoxy composite of the present invention.
• FIG. 7C is a magnified image of the DEP aligned KNN-epoxy composite of FIG. 7B.
• FIG. 7D is a SEM image of an unaligned (random) 0-3 composite.
• FIG. 9 are graphs of concentration of the structured KNN composite of the invention and an unstructured 0-3 composite, in vol% and theoretical models versus the piezoelectric charge coefficient of the composites d 33 .(pC/N).
• FIG. 10 are graphs of concentration the structured KNN composite of the invention and an unstructured 0-3 composite in vol% versus piezoelectric voltage coefficient of the composites (g 33 (mV.m/N)).
• FIG. 11 are graphs of concentration of the structured KNN composite of the invention and PZT-507 versus piezoelectric voltage coefficient g 33 (mV.m/N). DETAILED DESCRIPTION OF THE INVENTION
• a two-stage calcination process was discovered in the context of the present invention that allows for the production of lead-free lithium doped potassium sodium niobate piezoelectric particles that have a single crystalline phase. These produced particles have piezoelectric properties comparable to PZT-based particles with the added benefit of being lead-free.
• the ceramic piezoelectric materials the present invention can have a formula of (K,N) x Lii -x Nb03.
• x can be 0.05 ⁇ x ⁇ 0.07.
• the ceramic material can be phase pure crystals with uniaxial cubical particle morphology.
• the ceramic material can have a particle size distribution of 0.1 microns ⁇ d 10 ⁇ 5 microns, 1 micron ⁇ d 5 o ⁇ 10 microns, 5 microns ⁇ d 90 ⁇ 20 microns. In a particular embodiment, the ceramic material has a of 9 to 10.
• Non-limiting values for the d 5 o particle size value of the crystals are 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, .3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1., 7.2, 7.3, 7.4, 7.6, 7.8, 7.9, 8.0, 8.1., 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5
• a method of making the ceramic piezoelectric materials of the present invention involves a solid state synthesis of the materials that incorporates a two stage calcination step.
• FIG. 1 see also the Examples
• a flow chart of a method 100 of producing a highly crystalline ceramic (KNN or doped KNN) materials having a pervoskite structure is described.
• the ceramic precursors are obtained.
• the ceramic piezoelectric precursors can include potassium carbonate, sodium carbonate, niobium oxide, and lithium carbonate particles.
• the ceramic precusors are commercial available from many commercial chemical suppliers, for example, Sigma Aldrich®.
• the ceramic precursors e.g., Na,K,Li carbonates and ⁇ C
• the ceramic precursors are mixed under conditions sufficient to refine the particles size of the powders and form an agglomerate-free homogeneous powder.
• Mixing can be done using any known mixing unit suitable to reduce the particle size of the powders and provide a homogeneous powder free of metal containments. Examples of mixing units include a ball mill, a high speed stirrer, an ultrasound mixer or combinations thereof.
• a preferred mixing unit is a ball mill with zirconia milling media (e.g., milling balls). The use of zirconia balls can limit unwanted metal contamination of the powders. In some aspects, a milling medium can be used to aid refinement of the particle size of the ceramic precursors.
• Non-limiting examples of milling medium include organic solvents (for example, cyclohexane, glycols, propanol, hexane or the like), water, or any combination thereof.
• the ceramic precursors can be milled for as long as needed to produce the desired particle size (e.g., 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more hours). In a preferred embodiment, the ceramic precursors are milled as slurry in cyclohexane for about 3 hours.
• the liquid medium can be removed under conditions sufficient to remove the liquid medium, but less than the calcination temperature (e.g., 100 °C to 160 °C, or 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C or 160 °C for 1 to 5 hours, with 150 °C at 3 hours being preferred).
• the calcination temperature e.g., 100 °C to 160 °C, or 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C or 160 °C for 1 to 5 hours, with 150 °C at 3 hours being preferred.
• K 2 (C0 3 ) + Na 2 (C0 3 ) + Li 2 (C0 3 ) + Nb 2 0 3 ⁇ (K,Na,Li)Nb0 3 .
• the homogeneous, agglomerate-free ceramic precursor material is placed in a heating apparatus and heated in the presence of an oxidant (e.g., air or oxygen) at a specified rate (e.g., 1 °C, 2 °C, 3 °C, 4 °C, or 5 °C per minute) to a first calcination temperature.
• an oxidant e.g., air or oxygen
• a specified rate e.g., 1 °C, 2 °C, 3 °C, 4 °C, or 5 °C per minute
• the material is held at the first calcination temperature for a desired period of time (for example, 1, 2, 3, 4, 5, 6 7, 8, 9, 10 hours, with 3 hours being preferred).
• the first calcination temperature can be below the sintering temperature of the alkali metals (e.g., less than about 1100 °C), but high enough to promote formation of a crystalline ceramic structure with substantially a single crystalline phase. In one instance, no secondary phases are present.
• the first calcination average temperature can be greater than 950 °C, 955 °C, 960 °C, 965 °C, 970 °C, 975 °C, 980 °C, 985 °C, 990 °C, 995 °C, 1000 °C, 1005 °C, 1010 °C, or any value there between or an average temperature ranging from greater than 950 °C to 1010 °C, 960 °C to 1005 °C, or 980 °C to 1000 °C, with 1000 °C being preferred.
• step 108 after heating at the first calcination temperature for a desired period of time (e.g., 1000 °C for 3 hours), the crystalline ceramic material is cooled to ambient temperature by circulating ambient air through the heating apparatus (e.g., free cooling).
• step 110 the ceramic material is removed from the heating apparatus and milled in the mixing apparatus for a period of time sufficient to reduce the particle size to refine the particle size to submicron size (e.g., a d 5 o of less than 1 micron, 0.9, 0.8, 0.7, 0.6, 0.5 microns or less).
• the milled ceramic material is heated at a specified rate (e.g., 1 °C, 2 °C, 3 °C, 4 °C, or 5 °C per minute) per minute in the presence of an oxidant (e.g., air or oxygen) to a second calcination temperature for a desired period of time (for example, 1, 2, 3, 4, 5, 6 7, 8, 9, 10, 11, 12, 15 hours, with 10 hours being preferred).
• a specified rate e.g., 1 °C, 2 °C, 3 °C, 4 °C, or 5 °C per minute
• an oxidant e.g., air or oxygen
• the second calcination temperature is lower than the first calcination temperature, but sufficiently elevated to allow the submicron size particles to crystallize together and form a ceramic material of phase pure crystals with uniaxial cubical particle morphology.
• LiKNN crystals e.g.
• the second calcination average temperature can be less than 1000 °C, 995 °C, 990 °C, 985 °C, 980 °C, 975 °C, 970 °C, 965 °C, 950 °C, 955 °C, 900 °C, or any value there between or an average temperature ranging from greater than 900 °C to 1000 °C, 920 °C to 975 °C, or 930 °C to 950 °C, with 900 °C to 950 °C being preferred.
• step 114 after heating at the second calcination temperature for a desired period of time (e.g., 900 to 950 °C for 10 hours), the ceramic crystalline material is cooled to ambient temperature by circulating ambient air through the heating apparatus (e.g., free cooling).
• ambient air e.g., free cooling
• the two step calcination process with cooling to ambient temperature between the steps in the presence of oxidant controls the formation of the crystal structure which results in the particles having a pure phase crystalline structure with a controlled shape (e.g., uniaxial cubical morphology).
• the crystalline ceramic material can be removed from the heating apparatus and the crystals can be deagglomerated using known deagglomeration methods (e.g., ultrasonicating the crystals) for a sufficient amount of time (e.g. 0.25, 0.5, 1, 1.25, 1.5, 2 hours).
• the crystals can be mixed with a liquid medium to assist in the deagglomeration process. In some instances, deagglomeration is not necessary. Any ultrasonicating or milling medium known in the art or described herein can be used, with cyclohexane being preferred.
• the crystalline ceramic material can be removed from the deagglomeration unit.
• the particles can be filtered and/or dried under conditions sufficient to remove the medium (e.g., 100 °C to 160 °C for 1 to 5 hours, with 150 °C at 3 hours being preferred).
• the resulting ceramic materials e.g., KNN or LiKNN
• KNN or LiKNN can be used to make one or more piezoelectric materials and/or stored under dry conditions.
• the ceramic piezoelectric materials of the invention can be used to make a variety of piezoelectric composites.
• the piezoelectric composites can have various types of connectivity with the geometry of the composite being based on the connectivity. For example, for two-phase composite systems there are ten types of connectivity and for three to four phase systems there can be 20 to 35 types of connectivity. Geometry and connectivity designs can be done using known piezoelectric composite methods.
• FIG. 2A and 2B show two types of connectivity for a two phase composite system.
• FIG. 2A is a schematic of a 0-3 type connectivity.
• FIG. 2B is a schematic of a 1-3 type connectivity. Referring to FIG.
• the composite 200 with 0-3 has piezoelectric particles 204 randomly dispersed within the polymer matrix 202.
• the matrix 202 can be connected to itself in all three spatial directions, while the particles 204 lack contact.
• effective medium (EM) theory portrays the hulk, or apparent properties of these composites as isotropic.
• the composite can include the piezoelectric ceramic materials of the present invention described throughout the specification and a polymer matrix.
• the polymer matrix can include thermoset or thermoplastic polymers.
• Some non-limiting examples include epoxy resin, an unsaturated polyester resin, a polyurethane, bakelite, duroplast, urea- formaldehyde, diallyl-phthalate, an epoxy vinylester, a polyimide, a cyanate ester of polycyanurate, dicyclopentadiene, a phenolic, a benzoxazine, co-polymers thereof, or blends thereof.
• epoxy resin is used.
• a two component epoxy system is used, with diglycidyl ether bisphenol-A and polyoxypropylene diamine being a preferred.
• diglycidyl ether bisphenol-A and polyoxypropylene diamine are commercially available from Epoxy Technology, Inc. Billerica, MA USA) and/or SABIC Innovative Plastics (USA).
• the composite material can include thermoplastic polymers which can become pliable or moldable above a specific temperature, and return back to a more solid state upon cooling. There are a wide range of various thermoplastic polymers, and blends thereof that can be used to make a composite layer or material of the present invention.
• Some non-limiting examples include polyethylene terephthalate (PET), a polycarbonate (PC) family of polymers, polybutylene terephthalate (PBT), poly(l,4-cyclohexylidene cyclohexane-l,4-dicarboxylate) (PCCD), glycol modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and their derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomers, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PSS), sulfonates of poly
• the composite can be made using known methods to make piezoelectric composites.
• the amounts of polymer matrix and piezoelectric materials can be determined such that from 5% to 90%, 10% to 80%, or 20% to 50% by volume of the ceramic composite is piezoelectric materials.
• a non-limiting example includes mixing the ceramic piezoelectric materials of the present invention with a polymer matrix described above and throughout the specification at a high rate of speed (e.g., 2500 rpm, 3000 rpm, 3500 rpm, etc.) for a desired amount of time.
• the dispersion can be cured (e.g., hardened) during shaping by using agents and/or conditions appropriate for thermosets or thermoplastic polymer systems.
• Non- limiting examples of curing include cooling, UV curing, heat accelerated curing or compression curing of the dispersion.
• an epoxy resin and ceramic particles were mixed together for a desired amount of time, hardener added, and the mixed again, followed by degasing in vacuum for 10 minutes to form an unstructured composite having a 0-3 connectivity.
• the piezoelectric composite can be shaped using injection molding, extrusion, compression molding, blow molding, thermoforming or other known methods.
• the piezoelectric composite 200 can have orthotopic or transversely isotropic (e.g., 1-3 connectivity) as the piezoelectric ceramic materials have structural organization.
• Structural organization can be done using methods known in the art. On example includes wafering the ceramic materials 202 into rod-like structures 206, and backfilling the voids with intended material. Others entail weaving fibers of the ceramic material through a semi-porous matrix or manually aligning long fibers of the ceramic material 202 and then filling the surrounding area with the composite matrix 204, These techniques result in the ceramic material 202 forming continuous columns 206 that span the thickness of the composite.
• Non-uniform electric fields can be used to structure the ceramic particles 202 using dielectrophoresis to force the ceramic particles into columns 206.
• the dielectrophoresis is based upon the surface charges induced on dielectric particles in an electric field, and the interactions between the polarized particles and the applied electric fields.
• Structured 1-3 composites can be created by utilizing the dielectrophoretic force while the matrix material 204 is still fluid. While the inclusions are still mobile, the dielectrophoretic force structures them into column-like structures 206 (chains), where they are held until the composite matrix has solidified.
• this technique successfully creates 1-3 structured composites using manufacturing techniques similar to those for 0-3 materials.
• Using dielectrophoresis with the ceramic piezoelectric materials of the present invention results in the creation of composites with 1-3 connectivity that are lead-free and exhibit an increase in dielectric, piezoelectric, and mechanics, properties compared to 0-3 composites.
• Other methods include the use of piezoelectrophoresis.
• piezoelectrophoresis an externally applied electric field is applied at the same frequency with a cyclic hydrostatic pressure can result in the creation of "chains" and 1 -3 structured composites. This field care be applied in phase or out of phase, depending on the materials utilized.
• the unstructured composite can be subject to dielectrophoresis during the early stage of curing.
• a non-limiting example includes applying an alternating voltage across a dispersion of ceramic particles shortly after the hardener has been added to the epoxy resin.
• the piezoelectric ceramic composites made using the piezoelectric ceramic materials of the present invention and polymer matrixes described throughout the specification are lead free. Such a composite includes 5% to 50% by volume of the piezoelectric ceramic material.
• a charge constant for the piezoelectric ceramic (d 33 (pC/N)) can range from 10 to 14, or 10, 11, 12, 13, 14, with 12 being preferable.
• the composite can have a dielectric constant ( ⁇ 33 (-) ) of 13 to 17, or 13, 14, 15, 16, 17, with 15 being preferred.
• the piezoelectric voltage constant (g 33 (mV.m/N)) of the composite can range from 90 to 110, or 95 to 100, or 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, with 98 being preferred.
• the piezoelectric composites of the present invention are highly improved as compared to composites which were processed in a conventional way and have comparable properties to lead containing composites ⁇ See, for example, values in Table 3).
• the piezoelectric composite materials can be used in all types of applications and devices that utilize piezoelectric properties.
• Non-limiting examples include piezoelectric devices such as piezoelectric sensors, piezoelectric transducers, or piezoelectric actuators. These devices can be utilized in medical diagnostics, industrial automation, defense, and communication systems and the like.
• FIG. 3 is a graphical depiction of the two-stage calcination process of the present invention.
• FIG. 4 are XRD patterns of Samples 1-4 and 6.
• Data line 400 is Sample 1
• data line 402 is Sample 2
• data line 404 is Sample 3
• data line 406 is sample 4
• data line 408 is Sample 6. From the XRD patterns, the samples have similar diffraction patterns except that Samples 3, 4 and 6 exhibited a defined secondary phase (peaks, 112 and 202) with sample 6 having the sharpest peaks.
• the XRD analysis confirmed the development of pervoskite phase (secondary phase) for powders calcined at 1000 °C for 6 hours (Sample 4), 1100 °C for 3 hours (Sample 3), and the double calcined sample (Sample 6).
• the particle size distribution and morphology of the (K,Na) x Lii -x Nb03 powders were analyzed using a particle size analyzer and scanning electron microscopy (SEM, JEOL, JSM-7500F).
• FIG. 5 are graphs of particle size in micrometers versus volume percent for Samples 1 (data line 500), 2 (data line 502) and 6 (data line 504). Table 2 lists the particle size distribution for Samples 1-3, 5 and 6.
• FIG. 6A-E are SEM micrographs of Samples 1-3, 5 and 6.
• FIG 6A is a SEM micrograph of Sample 1
• FIG. 6B is a SEM micrograph of Sample 2
• FIG. 6C is a SEM micrograph of Sample 3
• FIG. 6D is a SEM micrograph of sample 5
• FIG. 6E is an SEM micrograph of Sample 6.
• the first high temperature calcination step formed the crystal structure without secondary phases.
• the submicron size particles crystallize together to form a second crystal structure have micron size cubical particles as shown in FIG. 6D and 6E.
• the epoxy resin and piezoelectric ceramic particles were mixed together using a high speed mixer (Speed Mixer DAC 150 FVZ) at 3000 rpm for 3 minutes after which the hardener was added and the composite resin was mixed again at 3000 rpm at 5 minutes followed by degasing in vacuum for 10 minutes to form unstructured 0-3 composites 1, 2, 3, 5, and 6 from piezoelectric ceramic samples 1, 2, 3, 5 and 6.
• the unstructured composite 0-3 samples was prepared were molded into circular disc shaped samples.
• FIG. 7A is a SEM tomography image DEP aligned LiKNN-epoxy composite.
• FIG. 7B is an SEM image DEP aligned LiKNN-epoxy composite.
• FIG. 7C is a magnified image of the DEP aligned KNN-epoxy composite of FIG. 7B
• FIG. 7D is a SEM image of an unaligned (random) 0-3 composite.
• Table 3 lists the piezoelectric properties of the structured composites of the invention (sample 5 and 6) and unstructured 0-3 composites (Sample 1-3). Table 3
• FIG. 10 are graphs of structured composites of the present invention (data line 1000) and 0-3 composites in vol.% (data line 1002) versus piezoelectric voltage coefficient of the composite (g 33 (mV.m/N)).
• FIG. 11 are graphs of concentration of the structured LiKNN composite of the invention (data line 1100) and a PZT-507 (PbZrTi) composite data line (1102) versus piezoelectric voltage coefficient g 33 (mV.m/N). From the data, it can be concluded that a two-step calcination method to fabricate well-defined morphological structures for lead-free ceramics has been demonstrated. The composites made by this method have highly improved piezoelectric properties as compared to composites which are processed using conventional methods. Table 4 lists the electrical properties of the composite sample 6 and publically available Thus, lead free piezoelectric composites can be made that have properties comparable to lead containing composites. Table 4

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