The Effects of Ba0.85Ca0.15Zr0.1Ti0.9O3 Addition on the Phase, Microstructure, and Thermoelectric Properties of Ca3Co4O9 Ceramics

In this work, the influences of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) addition on phase, microstructure, and thermoelectric properties of Ca3Co4O9 (CCO) were investigated. (1-x)CCO-(x)BCZT ceramics where x = 0, 0.003, 0.005, and 0.010 were fabricated successfully via a conventional solid-state sintering at 1,223 K for 24 hrs. The substitution of BCZT introduced the chemical defects (V''Co, V'''Co, V''Ca) in CCO ceramic, which increased charge carrier concentration and enhanced the electrical conductivity. The presence of Co3+ improved the Seebeck coefficients of CCO ceramic. The thermal conductivity of CCO ceramic decreased when BCZT was added. The addition of BCZT at x = 0.010 promoted the highest thermoelectric power factor (PF~235 mW/mK2), and the highest figure of merit (ZT~0.5) at 800 K, which present this ceramic an alternative p-type oxide thermoelectric for a high-temperature thermoelectric device.

Dielectric, ferroelectric and optical properties of Na and Nb co-doped (Bi0.5Na0.5)0.94Ba0.06TiO3

[(Bi0.5Na0.5)0.94Ba0.06]1-xNaTi1-xNbO3 (x = 0.5 and 0.10) ceramics were prepared via conventional solid-state sintering route. X-ray diffraction analysis of the samples exhibited the formation of the cubic structure. Similar structure was observed from the Raman spectra of the samples. The optical band gap of the samples slightly decreased from 3.08 to 3.06 eV with increasing level of Na+ and Nb5+. The addition of Na+ and Nb5+ shifted Tm towards room temperature (RT). The sample x = 0.05 had a stable relative permittivity ɛr(mid) = 3914 across the temperature range 79-350 ℃ and tanδ < 0.025 (104-279 ℃). The energy density of sample with x = 0.05 was 0.4 J/cm3 which decreased to 0.32 J/cm3 at an applied electric field of 50 kV/cm with further substitution of Na+ and Nb5+ (i.e., x = 0.10).

Interdiffusion and Intermetallic Compounds at Al/Cu Interfaces in Al-50vol.%Cu Composite Prepared by Solid-State Sintering

Al–Cu composites have attracted significant interest recently owing to their lightweight nature and remarkable thermal properties. Understanding the interdiffusion mechanism at the numerous Al/Cu interfaces is crucial to obtain Al–Cu composites with high thermal conductivities. The present study systematically investigates the interdiffusion mechanism at Al/Cu interfaces in relation to the process temperature. Al-50vol.%Cu composite powder, where Cu particles were encapsulated in a matrix of irregular Al particles, was prepared and then sintered at various temperatures from 340 to 500 °C. Intermetallic compounds (ICs) such as CuAl2 and Cu9Al4 were formed at the Al/Cu interfaces during sintering. Microstructural analysis showed that the thickness of the interdiffusion layer, which comprised the CuAl2 and Cu9Al4 ICs, drastically increased above 400 °C. The Vickers hardness of the Al-50vol.%Cu composite sintered at 380 °C was 79 HV, which was 1.5 times that of the value estimated by the rule of mixtures. A high thermal conductivity of 150 W∙m−1∙K−1 was simultaneously obtained. This result suggests that the Al-50vol.%Cu composite material with large number of Al/Cu interfaces, as well as good mechanical strength and heat conductance, can be prepared by solid-state sintering at a low temperature.