Structural studies & thermal expansion behavior of samarium Uranate at HP-HT

Sm6UO12 has been synthesized by urea-combustion method and characterized using synchrotron x-ray source. The compound is found to be in single phase crystallizing in rhombohedral lattice with lattice parameters a = 10.153 Å and c = 9.625 Å. High-pressure experiment at ambient temperature reveals the lattice to be stable up to 27.0 GPa. The bulk modulus of the compound is found to be 157.0 GPa. At higher pressures, reflections broaden out as a result of disorder in the system, leading to amorphization at further higher pressures. High pressure and high temperature (HP-HT) x-ray diffraction studies have been carried out up to 6.0 GPa and 673 K. A softening is seen in the material at HP-HT resulting in lower bulk modulus at high temperature. Volume thermal expansion coefficients are found to be 22 × 10−6 K−1 and 17.7 × 10−6 K−1 in the temperature range 298 K–473 K and 298 K-673 K, respectively. •The compressibility in RE6UO12 is found to increase along Rare-earth series.•Contrary to temperature effect, a-axis is more rigid under pressure than c-axis.•Disorder in anions followed by that of cations is seen at high pressures.•Decrease in thermal expansion coefficient with respect to pressure is observed.