Templated Grain Growth Process Research Articles

Superior Large-Signal Piezoelectric Coefficient in Textured NBT-Based Piezoceramics by Template-Induced Structure and Composition Modulation.

The field-induced-phase transition in (Na1/2Bi1/2)TiO3-based lead-free piezoceramics can be facilitated in the ⟨001⟩-crystallographic orientation, and the templated grain growth is an effective method to align polycrystalline ceramics along with specific directions. However, due to the low texturing degree and undesirable composite effect of the added templates, the textured ceramics using the templated grain growth (TGG) method usually require a higher driving field to trigger the phase transition instead. Here, ⟨001⟩-textured (Na0.5Bi0.5)0.935Ba0.065Ti0.978(Fe0.5Nb0.5)0.022O3 ceramics are prepared through a liquid-phase-assisted TGG process at a low sintering temperature (1000 °C), in which the NaNbO3 (NN) templates induce a strong crystallographic anisotropic structure (a high Lotgering factor of 95%) while dissolving into oriented grains. The dissolution of templates acts as a composition doping and contributes to reducing the driving electric field as proven by the phase-field simulation analysis. Furthermore, electrical and structural characterizations reveal that an increased ionic disorder occurs in the textured ceramic, causing highly dynamic polar nanoregions and a larger reversible phase transition. Thanks to the appropriate structure/composition control, the textured ceramic achieves a large d33* value of 907 pm/V at 40 kV/cm. The high-performance lead-free ceramic under low driving electric field benefits the development of multilayer piezoelectric actuators.

Optimisation of the Zr:Ti ratio in bulk lead zirconate titanate for templated grain growth using BaTiO3 seeds

Presented here is a proof of concept demonstration of the templated grain growth (TGG) process for the development of [001]c fibre-textured Pb(ZrxTi1-x)O3 (PZT) ceramics. BaTiO3 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 BaTiO3 dissolution into the matrix. Solid solution incorporation of BaTiO3 during sintering resulted in a structural shift away from the PZT morphotropic phase boundary (MPB) and a decrease in Curie temperature (TC) 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(Zr0.56Ti0.44)O3 resulted in a final bulk Pb0.947Ba0.053(Zr0.531Ti0.469)O3 ceramic having MPB-like properties of d33 = 453 pC/N, tan δ = 0.017, TC = 340 °C, and Ec = 9.3 kV/cm, which was observed to be similar to commercial ‘soft’ PZT-5A1.

Texturing of hydrothermally synthesized BaTiO3 in a strong magnetic field by slip casting

Barium titanate powder was processed by slip casting in a rotating strong magnetic field of 9.4T. The orientation factor of the sintered compact was analyzed by the X-ray diffraction technique and the microstructure (grain-size) was analyzed by scanning electron microscope. The hydrothermally prepared barium titanate was used as matrix material and the molten-salt synthesized barium titanate, with a larger particle-size, was used as template for the templated grain-growth process. Addition of large template particles was observed to increase the orientation factor of the sintered cast (5vol% loading). Template particles acted as starting grains for the abnormal grain-growth process and the average grain-size was increased after sintering. Increasing the solid loading (15vol%) resulted in a similar orientation factor with a decrease of the average grain-size by more than half. However, addition of templates to the 15vol% cast had a negative effect on the orientation factor. The impingement of growing particles was stated as the primary cause of particle misorientation resulting in a low orientation factor after sintering. Different heating conditions were tested and it was determined that a slow heating rate gave the highest orientation factor, the smallest average grain-size and the highest relative density.

Templated Grain Growth in Macroporous Materials

We demonstrate a facile method to produce crystallographically textured, macroporous materials using a combination of modified ice templating and templated grain growth (TGG). The process is demonstrated on alumina and the lead‐free piezoelectric material sodium potassium niobate. The method provides macroporous materials with aligned, lamellar ceramic walls which are made up of crystallographically aligned grains. Each method showed that the ceramic walls present a long‐range order over the entire sample dimensions and have crystallographic texture as a result of the TGG process. We also present a modification of the March–Dollase equation to better characterize the overall texture of materials with textured but slightly misaligned walls. The controlled crystallographic and morphologic orientation at two different length scales demonstrated here can be the basis of multifunctional materials.

Electrical Properties of Ag-Doped 0.94(K0.5Na0.5)NbO3-0.06LiNbO3 Ceramics Prepared by Templated Grain Growth

In this study, we have investigated the current-voltage characteristics of Ag-doped 0.94(K0.5Na0.5)NbO3-0.06LiNbO3 lead-free piezoelectric ceramics, prepared by a template grain growth (TGG) method employing cubic (K,Na)NbO3 single crystal seeds as templates. It is well known that TGG methods can improve piezoelectric properties by increasing the grain size during the sintering process. The X-ray diffraction of the sample at room temperature showed perovskite structure. Scanning electron microscopy (SEM) showed great differences in both grain shape and size between the TGG-processed ceramic and the conventionally prepared ceramic. The leakage current density of Ag-doped 0.94(K0.5Na0.5)NbO3-0.06LiNbO3 ceramic prepared by the TGG process was reduced. The current-voltage characteristics according to varying temperature provide us with the temperature-dependent resistance and temperature coefficient of resistance in the ceramics prepared in this study. The true leakage currents and different types of dipole motions of the ceramic are also discussed.

A critical evaluation of reactive templated grain growth (RTGG) mechanisms in highly [001] textured Sr0.61Ba0.39Nb2O6 ferroelectric-thermoelectrics

Abstract

Fabrication of Na0.5Bi0.5TiO3–BaTiO3‐Textured Ceramics Templated by Plate‐Like Na0.5Bi0.5TiO3 Particles

Textured 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 (NBT–6BT) ceramics were fabricated by templated grain growth (TGG) using anisotropically shaped Na0.5Bi0.5TiO3 (NBT) templates. Platelet NBT was synthesized by the topochemical technique, using precursor Na0.5Bi4.5Ti4O15 (NBIT). The NBT particles have an average length of 10–15 μm and a thickness of 1 μm, which are suitable templates for obtaining textured ceramics (especially NBT‐based ceramics) by the TGG process. This study revealed that the NBT templates are effective in inducing grain orientation in NBT–6BT ceramics. For NBT–6BT ceramics textured with 5 vol% NBT templates, a Lotgering factor of 0.87 and a d33 of 299 pC/N are given.

Fabrication of Lead-Free Piezoelectric Ceramics by (Reactive) Templated Grain Growth

The controlled development of texture in polycrystalline materials is a topic of recent interest in ceramic processing, since it allows improved tailoring of piezoelectric properties. One promising route for controlled texture development is templated grain growth (TGG). The TGG process is dependent on the formation of oriented particles by in situ reaction precursor particles with aligned shape anisotropy templates. It has been shown that ferroelectric/piezoelectric ceramics with a high degree of texture along the polar direction exhibit a good performance. However, how to get the excellent performance with high texture, how to synthesize the plate like template suitable for the ceramics, many issues remain to be overcome for these texture ceramics fabricated by TGG. This article reviews the current literature and patent base of TGG technique of Bismuth Sodium Titanate Bi0.5Na0.5TiO3 (abbreviated as BNT) based ceramic materials which is one group of promising lead free material to replace the widely used lead based perovskite materials. Keywords: Templated grain growth, texture, piezoelectric ceramic

Piezoelectric Properties of SrBi2Nb2O9 Textured Ceramics

The textured ceramics of the bismuth layer structured ferroelectrics SrBi2Nb2O9 (SBN)-type compound were fabricated by the templated grain growth (TGG) method, and their characteristics and piezoelectric properties were studied. Platelike particles with a large shape anisotropy, which were needed as template particles in the TGG process, were obtained for the composition with 10% Nd substitution on the Sr site of SBN. Highly (00ℓ) textured Sr0.9Nd0.1Bi2Nb2O9 (SNBN) ceramics were successfully obtained using the TGG process with platelike particles, and the orientation degree of the textured ceramics was 96%. The electromechanical coupling factor of the 96% orientation degree textured ceramics in the thickness shear vibration mode was three times as large as that for the randomly oriented ceramics. The temperature coefficient of the resonant frequency (TCF) of the textured ceramics was +20.9 ppm/°C, whose absolute value was two-thirds of that of the randomly oriented ceramics. The resonant frequency of the textured ceramics increased with temperature, while the resonant frequency of the randomly oriented ceramics decreased with increasing temperature. This result indicated the possibility of obtaining an excellent TCF by the optimization of grain orientation. Therefore, textured ceramics with orientation degrees from 54% to 96% were prepared using template particles of different average diameters, and an excellent TCF of -0.4 ppm/°C was obtained for the specimen with an orientation degree of 76%.

Texture Development in KSr<sub>2</sub>Nb<sub>5</sub>O<sub>15</sub> Ceramics Fabricated by Reactive Templated Grain Growth

Texture Development in KSr<sub>2</sub>Nb<sub>5</sub>O<sub>15</sub> Ceramics Fabricated by Reactive Templated Grain Growth