The structure of LaTaO₄ at 300°C by neutron powder profile analysis

LaTaO₄ above 175°C is orthorhombic, space group A2₁am, with a = 5.6643(1), b = 14.6411(3), c = 3.9457(1), and Z = 4. It is isostructural with room temperature BaMnF₄. The structure, refined by the Rietveld powder profile analysis technique to a final agreement index of 8.6%, consists of sheets of corner shared TaO₆ octahedra extending perpendicular to b, bonded to each other parallel to b by the nine coordinated lanthanum ions. All atoms are in position (x, y, 0) with coordinates: La (0.1788, 0.1676), Ta (0.2192, 0.4141, O1 (0.4216, 0.3008), O2 (-0.0486, 0.3380), O3 (0.5614, 0.4689), O4 (0.2496, 0.9153). Orthorhombic CeTaO₄ and PrTaO₄ are isostructual.