Investigations of thermal conductivity in nano-crystalline Gd2Ti2O7 pyrochlore

Pyrochlore ceramics with chemical formula A(2)B(2)O(7) (A= rare earth, B= tetravalent metal) have extremely low thermal conductivities (kappa) and are thought to be promising candidates for thermal barrier coatings (TBCs) applications. This study reports kappa for nanocrystalline (nc) Gd2Ti2O7 pyrochlore fabricated by spark plasma sintering followed by sintering at different temperatures to better understand their thermal properties. The structural analysis confirmed the synthesis of single-phase nc-Gd2Ti2O7 pyrochlore. The thermal conductivity investigations displayed a systematic decrease in thermal conductivity from 1.6 Wm(-1)K(-1) to 0.6 Wm(-1)K(-1) for the sample sintered at a lower temperature due to high porosity. The value of the kappa is found to decrease sublinearly (kappa proportional to T-alpha, where 0 < alpha < 1) with temperature for all the nc-Gd2Ti2O7 pyrochlore samples. DFT- GGA calculation exhibits that the nc-Gd2Ti2O7 is a direct band gap at the Gamma point of the Brillouin zone, and its value is increased with the sintering temperature. In addition, the effect of sintering temperature on the specific heat capacity (C-p) is insignificant in nc-Gd2Ti2O7 structures, as confirmed by the quasi-harmonic approximation. Theoretical and experimentally determined results are in good agreement, and values are compatible with the thermal insulation requirements for various applications.