By Deepam Murya
1. Design and fabrication of new materials with high dielectric constant for multilayer ceramic capacitors (MLCCs)
We designed new modified BaTiO3 material for Y5V type capacitor application. In order to get volume efficiency of MLCCs, the grain size of the material should be in submicron regime (Fig-1) and at the same time material should have high dielectric constant (Fig. 2) at room temperature with low temperature coefficient of capacitance (TCC). Various properties of these materials are listed in Table -1.
2. Compositionally graded composites
We prepared compositionally graded composite (Fig.3) and studied the effect of interface on the ferroelectric response. Fig. 4(a-c) represents SEM image of sharp interface and Fig. 4(d) represents the domain structure across the interface of these compositionally graded composites with different domain width.
The PE –hysteresis loop measured on various laminate composites are provided in Fig. 5. The effect of composite structure is clearly observed in PE hysteresis on various specimens. Trilayer specimen was found to exhibit double loop behavior due finite coupling across the interface.
3. Synthesis of Na0.5Bi0.5TiO3-BaTiO3 (NBTBT) ceramics using Na2 Ti6O13 (NaTiO) whiskers
NBTBT is an important lead free piezoelectric material. We synthesized NBTBT materials with good piezoelectric properties using NaTiO whiskers as starting materials and thoroughly studied microstructural evolution mechanism and sintering behavior. Fig.6 represents the HR-TEM microstructure of the NaTiO whiskers and schematic representation of octahedra connectivity.
After aligning NaTiO whiskers in base matrix powder of NBTBT using tape casting method and processing at high temperature, the specimen transformed to NBTBT phase after liquid phase sintering. A HRTEM image of the specimen processed at 1175C (2 h) have been depicted in Fig.7, which represents localized phases due to chemical fluctuation during liquid phase sintering. These kind of localized also phases contributes to diffuse nature of phase transitions along with the polar nano regions (PNRs).
The growth of grains was found to be in <111>c direction resulting smaller (111)c plane. Also, the assumed equilibrium shape of grains was found to exhibit bigger faces with (100)c plane indicating the surface energy in <100>c direction is lower than that of <111>c direction (Fig. 8). Fig. 9 represents the AFM image of the growth steps confined preferably on the corners of grains. The step height of these growth steps was measured using AFM images.
4. Synthesis of Na0.5Bi0.5TiO3-BaTiO3 (NBTBT) textured ceramics and single crystal
We used TGG and RTGG method to synthesize textured NBTBT ceramics. However, NBTBT single crystals were prepared using flux growth method. EBSD orientation maps of textured and singe crystal NBTBT materials are given in Fig. 10.