Presented here is a proof of concept demonstration of the templated grain growth (TGG) process for the development of [001] c fibre-textured Pb(Zr x Ti 1- x )O 3 (PZT) ceramics. BaTiO 3 platelets (5 and 10 vol.%) were selected to seed growth of highly oriented PZT grains resulting in texture fractions as high as 94%. The TGG process in PZT was observed to be critically dependent upon the addition of excess PbO liquid phase and may be driven by BaTiO 3 dissolution into the matrix. Solid solution incorporation of BaTiO 3 during sintering resulted in a structural shift away from the PZT morphotropic phase boundary (MPB) and a decrease in Curie temperature ( T C ) by ~ 40 °C which still exceeded > 300 °C. Modification of the Zr:Ti ratio in untextured ceramic analogues was explored as a strategy to tailor dielectric, ferroelectric, and electromechanical properties. An initial PZT matrix composition of Pb(Zr 0.56 Ti 0.44 )O 3 resulted in a final bulk Pb 0.947 Ba 0.053 (Zr 0.531 Ti 0.469 )O 3 ceramic having MPB-like properties of d 33 = 453 pC/N, tan δ = 0.017, T C = 340 °C, and E c = 9.3 kV/cm, which was observed to be similar to commercial ‘soft’ PZT-5A1.

Additive manufacturing (AM) is a powerful tool for fabricating ceramics with novel and/or improved properties by enabling access to unique part architecture and geometry, and control of pore structure and distribution. In this review we show that layer-wise and direct writing AM processes can be used to fabricate microscopically-textured ceramics with unique crystallographic orientations by combining templated grain growth (TGG) with manipulation of the rheological properties of the feedstock, printhead geometry and printing speed during layer-wise and direct writing AM processes. For TGG the shear gradient, and resultant local torque, during printing aligns anisotropically-shaped template particles which serve as substrates for subsequent oriented grain growth and increase in crystallographic texture in the final part during sintering. We show how the deposition flow field and rheology of AM feedstocks coupled with anisotropic printing nozzles enables enhanced template alignment by impacting the torque gradient during deposition. Prospects for AM of textured ceramics are presented.

Calcination refers to the general class of thermal processes used to synthesize or prepare a ceramic powder before it is dispersed in a liquid, formed into a shape and densified by sintering. In general calcination is used to thermally decompose sparingly soluble metal oxide precursors such as metal carbonates, hydroxides and oxalates, or thermally react simple metal oxide powders to form a thermodynamically stable mixed metal oxide. For many ceramic powders both processes are needed. This article first outlines how the decomposition temperature depends on heat transfer and mass transport of product gases in individual particles and through the powder bed, and then discusses calcination of mixed oxide powders to form complex, mixed metal oxides. It is shown how thermodynamics and kinetics influence powder characteristics and how these processes can be manipulated by seeding to yield powders with targeted phases, particle size, and less aggregation.

Mn-doped PIN-PMN-PT ceramics were 90% [001]C textured by reactive templated grain growth (RTGG) with 5 vol% BaTiO3 microplatelets. Hardened properties such as high coercive field (EC) of 14 kV/cm, low dielectric loss (tan δ) of 0.37-0.66%, and high QM of 496 were obtained. Textured Mn-doped ceramics have TC of 219 °C, and a two times greater low-field d33* of 846 pm/V than random ceramics. Rayleigh analysis of textured PIN-PMN-PT ceramics shows that Mn-doping reduces the relative extrinsic contribution of the piezoelectric response to the strain behavior from 38% to 18% (at 4 kV/cm) by reducing irreversible domain wall motion. Mn-doping also reduced the overall strain response of PIN-PMN-PT, but crystallographic texturing increased the intrinsic piezoelectric response of the lattice as evidenced by the increase in d33 (Berlincourt) from 283 pC/N in random ceramics to 341 pC/N in textured ceramics. These results demonstrate that textured Mn-doped PIN-PMN-PT ceramics are excellent candidates for high-power transducer applications.

This study reports the effects of composition and the presence of residual template particles on the electromechanical properties of random and textured CuO-doped Pb(Yb1/2Nb1/2)O-3-Pb(Mg1/3Nb2/3)O-3-PbTiO3 ceramics. Fully textured PYN-PMN-PT ceramics were produced with [001]-oriented barium titanate (BT) particles. The strain of all textured compositions was improved by 40-82 %, and the coercive field was increased by-1 kV/cm relative to ceramic compositions. Textured 20PYN-46PMN-34PT ceramics had the best combination of properties including a high Ec of 9.8 kV/cm and a low strain hysteresis of 8.5 %. Rayleigh analysis of textured PYN-PMN-PT ceramics showed that more rhombohedral compositions have greater strain because of improved extrinsic and intrinsic contributions to the piezoelectric response. These results demonstrate that textured PYN-PMN-PT is a promising material for high power transducers, however compositions must be sufficiently on the rhombohedral side of the morphotropic phase boundary to compensate for the phase-shifting effects of residual stresses from residual BT template particles.

Direct writing is a unique means to align anisotropic particles for the fabrication of textured ceramics by templated grain growth (TGG). We show that alignment of tabular barium titanate (BT) template particles (20-40 mu m width and 0.5-2 mu m thickness) in a PIN-PMN-PT matrix powder (d(50) = 280 nm) is significantly improved during direct writing using anisotropic nozzles at high printing rates. The particle orientation distribution in as-printed filaments, and the texture orientation distribution in sintered ceramic filaments are shown to directly correlate with COMSOL Multiphysics-predicted torque distributions for direct writing with aspect ratio 2, 3 and 5 oval nozzles. Electromechanical strain properties of the textured piezoelectric ceramics significantly improved relative to random ceramics when printed with anisotropic nozzles. Simulations of aspect ratio 20 nozzles and nozzles with interior baffles demonstrate significantly increased torque and near elimination of constant shear stress cores (i.e. plug flow).

This paper explores the templated grain growth and texturing of Pb(Yb1/2Nb1/2)O-3-Pb(Mg1/3Nb2/3)O-3-PbTiO3(PYN-PMN-PT) ceramics. A PbO-CuO liquid phase was determined to substantially increase the growth of PYN-PMN-PT on barium titanate template particles. Texturing resulted in an 83% enhancement in strain behavior (754 pm/V) compared with random PYN-PMN-PT ceramics (413 pm/V). The increased Pb(Yb1/2Nb1/2)O-3(PYN) content of textured 21PYN-41PMN-38PT resulted in a high coercive field of 13.9 kV/cm. Residual barium titanate templates reduced the polarization from 33.7 to 26.2 mu C/cm(2)and slightly decreased the Curie temperature (236-224 degrees C). These results show that textured PYN-PMN-PT is a promising material for high strain and coercive field transducers.

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The effects of acceptor doping with manganese as either MnO(2)or MnNb2O6(MnN) with CuO on the dielectric, ferroelectric, and piezoelectric properties of PIN-PMN-PT ceramics were investigated. The 2% MnNb2O6-doped PIN-PMN-PT (6Pb(Mn1/3Nb2/3)O-3-25Pb(In1/2Nb1/2)O-3-34Pb(Mg1/3Nb2/3)O-3-35PbTiO(3)) ceramics possessed hard properties such as high coercive field (E-C) of 11.7 kV/cm, low dielectric loss (tan delta) of 0.7%, and high electromechanical quality factor (Q(M)) of 1011. These properties were diminished in MnO2-doped ceramics because of lower oxygen vacancy defect concentration, and exaggerated grain growth resulted in >20 mu m grain size. Co-doping with 2 mol% MnNb(2)O(6)and 0.5 mol% CuO retained hardened properties such as highE(C)of 9.6 kV/cm, low tan delta of 0.6%, and highQ(M)of 1029. MnNb2O6-doped and MnNb2O6 + Cu co-doped ceramics display excellent figures of merit for resonance and off-resonance applications as well as high energy conversion efficiencies which make them promising candidates for high-power transducer elements.

Relationships between sintering temperature and annealing atmosphere on microstructure and dielectric, ferroelectric, and piezoelectric properties of reactively sintered CuO-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics were investigated. Uniform 2−3 μm grain size, dense CuO-doped PIN-PMN-PT ceramics are obtained when oxygen sintered versus a bimodal grain size microstructure when sintered in air. Oxygen sintered ceramics have excellent properties including d33 = 300–315 pC/N, EC = 7.7–8 kV/cm, and tan δ < 1.5%. The MPB region was mapped for ternary compositions doped with 0.5 mol% CuO and sintered in O2. MPB 25PIN-40PMN-35PT demonstrated the maximum piezoelectric properties with d33 = 565 +/− 23 pC/N and kp = 0.64 +/− 0.01. Sintering from 1050 °C to 1200 °C increased the coercive field from 8.5 to 11.5 kV/cm and reduced dielectric losses from tan δ = 1.8% to 0.8% by facilitating diffusion of CuO into the lattice and creating domain wall pinning defect dipoles as evidenced by an increase in the internal field bias of P-E loops.

Controlling the rheology of direct writing pastes is essential for producing high quality printed ceramics. Ceramic pastes were formulated to explore the relation between surface chemistry and rheology of complex pastes of Pb(In1/2Nb1/2)O-3-Pb(Mg1/3Nb2/3)O-3-PbTiO3(PIN-PMN-PT) powder, large BaTiO3(BT) platelet particles, and a commercial poly(acrylic) acid-based binder system. Zeta potential of the ceramic powder, the conformation of the poly(acrylic) acid, and the effect of these factors on rheology were evaluated as a function of suspension pH. Effective dispersion and amenable rheology for direct writing were achieved at mixing pH 5. Additions of 0.3 to 2.6 vol% BT tabular particles dramatically altered the rheology of the pastes due to the shear alignment of the BT particles. Powder-organic interactions and the size and concentration of BT platelet particles can be tailored to direct write either space-filling filaments to form dense ceramics or non-flowing filaments to form spanning ceramic structures.

This work demonstrates damage tolerant behavior of ceramic laminates designed with residual stresses and free of surface edge cracks. Non-periodic architectures were designed by embedding 2 textured alumina (TA) layers between 3 equiaxed alumina-zirconia (AZ) layers. Compressive residual stresses of similar to 250 MPa were induced in the textured layers. Indentation strength tests showed that textured compressive layers arrested the propagation of cracks. Results were compared to periodic architectures with the same volume ratio of TA and AZ materials. Crack propagation was arrested in both periodic and non-periodic designs; the minimum threshold-strength being higher in the latter. Non-periodic architectures with compressive layers as thin as similar to 200 mu m showed no evidence of surface edge cracks, yet still reached minimum threshold strength values of similar to 300 MPa. In addition, the textured microstructure promoted crack bifurcation in the thin compressive layers and thus enhanced the damage tolerance of the material.

This study explores sintering and piezoelectricity of ZnO-doped perovskite Pb(In1/2Nb1/2)O-3-Pb(Zn1/3Nb2/3)O-3-PbTiO3 (PIN-PZN-PT) ceramics. The enhanced densification of ZnO-doped PIN-PZN-PT is attributed to the formation of oxygen vacancies by the incorporation of Zn2+ into the perovskite B-site and increased rate of bulk diffusion relative to undoped PIN-PZN-PT. Incorporation of Zn2+ into the perovskite lattice increased the tetragonal character of PIN-PZN-PT as demonstrated by tetragonal peak splitting and increased Curie temperature. Sintering in flowing oxygen reduced the solubility of Zn2+ in the perovskite lattice and resulted in rhombohedral PIN-PZN-PT. Sintering in oxygen prevented secondary phase formation which resulted in a high-piezoelectric coefficient (d(33) - 550 pC/N), high-coercive field (E-c - 13 kV/cm), and high-rhombohedral to tetragonal phase transition temperature (Tr-t - 165 degrees C). We conclude that ZnO-doped PIN-PZN-PT ceramics are excellent candidates for high-power transducer applications.

In Dr. Messing's assessment, "Dr.Göken brings extensive expertise

We have performed studies of the orientation distribution in < 001 >(C) textured, 0.03(Na1/2Bi1/2)TiO3 - 0.97[0.715Pb(Mg1/3Nb2/3)TiO3 - 0.285PbTiO(3)] (0.03NBT-0.97[PMN-28.5PT]) ceramics by a pole figure method, comparing the results to those for PMN-PT single crystal and polycrystal samples. The pole figures about the (001) zone are found to have monoclinic, Ma, phase for textured ceramics in the annealed condition and were similar to those for electrically poled single crystals. However, electrical poling of the textured ceramics resulted in a doublet splitting of the orientation distribution about the direction that defined the original grain texturing. Studies of pole figures about other high-symmetry zones also revealed the development of some degree of preferred orientation along the in-plane directions after poling. Our findings demonstrate that E-field induced phase transformation and domain textures superimpose with that of preferred grain orientations, giving rise to a unique texture symmetry for PMN-PT. The texture symmetry changes are driven by minimization of the elastic strain energy, and have an important effect upon the piezoelectric properties.

This paper reports on the phase formation of perovskite Pb(In1/2Nb1/2)O-3-Pb(Zn1/3Nb2/3)O-3-PbTiO3 (PIN-PZN-PT) powder when doped with 0.04 to 0.83mol% ZnO. Air calcination of undoped powder mixtures for 4hours at 800 degrees C resulted in a mixture of Pb2Zn0.29Nb1.71O6.565 pyrochlore, PIN-PZN-PT perovskite, and In2O3. ZnO dopant concentrations as low as 0.04mol% increased the rate of perovskite formation and resulted in near phase pure perovskite powder of 0.5m particle size when heated at 800 degrees C in air. In all cases PbTiO3 and Pb(In1/2Nb1/2)O-3 formed prior to PIN-PZN-PT formation. ZnO doping promotes perovskite phase formation by increasing the reactivity of the intermediate pyrochlore phase by substituting Zn2+ on Nb5+ sites and forming oxygen vacancies when heated in air. Heating in high PO2 resulted in an incomplete reaction and a mixture of perovskite and pyrochlore whereas low PO2 resulted in phase separation into a mixture of rhombohedral perovskite, tetragonal perovskite, and pyrochlore. The PO2 sensitivity clearly shows that oxygen vacancies due to ZnO-doping are critical for synthesis of phase pure PIN-PZN-PT powder.

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