Crystal structure of the high-pressure modification of NdTaO4

The crystal structure of the metastable NdTaO4 high-pressure modification (HPM) has been studied by X-ray powder diffraction. It was found that the crystal structure of HPM NdTaO4 belongs to the monoclinic LaTaO4-type structure (space group P21/c, a=7.5920(7) Å, b=5.4673(5) Å, c=7.7022(7) Å, β=100.032(6)°, Z=4). The difference in structure between LnTaO4 with Ln=Nd–Lu (fergusonite-type structure) and that with Ln=La–Pr (monoclinic LaTaO4-type structure) is most likely due to the difference in size of the rare-earth cations.