Physical, Dielectric Properties and Micro-Hardness of the (Ba_0.90Ca_0.10)_0.90(Na_0.50Bi_0.50)_0.10TiO₃ Ceramics Prepared by Molten Salt Method

Abstract

In this study, the physical properties, dielectric properties, and micro-hardness of (Ba0.90Ca0.10)0.90(Na0.50Bi0.50)0.10TiO3 or BCT-NBT ceramics prepared by molten salt method with various sintering temperatures were investigated. The powders were calcined at 500-1100°C for 4 h with heating rate of 5°C/min. It was found that the optimum calcination condition was 1000°C for 4 h. These powders were pressed and sintered at 1200-1400°C for 3 h with a heating rate of 5°C/min. The microstructure was examined by scanning electron microscope (SEM). The density of the sintered samples was measured by Archimedes method with distilled water as the fluid medium. Dielectric properties were examined by LCR meter. The micro-hardness of the BCT-NBT ceramics was determined using the Vickers and Knoop indentation techniques. The results showed that the average grain sizes increased with increasing sintering temperatures. At sintering temperatures higher than 1200°C, the fracture mode changed from partial intra-granular to mainly intra-granular. The sintering temperature at which the density, dielectric and hardness properties were maximal was 1350°C. The highest density was about 5.4 g/cm3, and the Vickers and Knoop micro-hardnesses were 6.6 and 6.4 GPa, respectively. The dielectric constant at the Curie temperature was 3682 and the dielectric loss was 0.01 at 1 kHz frequency.

Micromechanical characterization of microwave dielectric ceramic BaO–Sm 2O 3–5TiO 2 by indentation and scratch methods

“…The rapid development of wireless communication with the broadband network has significantly increased the demand for microwave dielectric ceramics of excellent dielectric behaviors (e.g., suitable relative permittivity, high quality factor, and low-temperature drift of resonance frequency [1][2][3]) together with high J u s t A c c e p t e d mechanical properties (e.g., elastic modulus, hardness, and fracture toughness [4][5][6][7]), since excellent mechanical properties (e.g., high cracking resistance [8][9][10][11] and penetration resistance [12,13]) can ensure high structural stability, high reliability and long-term service life of dielectric ceramics, and have drawn extensive attention in the field of dielectric ceramics [4][5][6]14]. Values of Meyer and Knoop hardness of dielectric ceramic (Ba0.9Ca0.1)0.9(Na0.5Bi0.5)0.1TiO3 were found to be almost the same, and both increased with increasing sintering temperature [15]. The dielectric ceramics Ba6-3xR8+2xTi18O54 (0 ≤ x ≤ 1, R denotes rare earth element such as Nd, Sm, La, and Pr) of tungsten bronze-type structure have been extensively applied in microwave devices due to their excellent microwave properties [16].…”