A neutron powder diffraction determination of the thermal expansion tensor of crocoite (PbCrO4) between 60 K and 290 K

The thermal expansion tensor of crocoite has been determined from high-resolution neutron time-of-flight powder diffraction data. The temperature dependence of the lattice constants between 4.5 K and 290 K have been fitted to a quasi-harmonic Einstein model, and the temperature dependence of the thermal expansion tensor has been calculated for 60 K less than or equal to T less than or equal to 290 K. The magnitudes of the principal expansivities and their orientation exhibit saturation behaviour for temperatures above 300 K. The predicted saturated expansion coefficients are alpha(11) = 33.1(1) x 10(-6)K(-1), alpha(22) = 15.72(3) x 10(-6)K(-1), alpha(33) = 3.36(1) x 10(-6)K(-1), with alpha(22) parallel to b and alpha(11) lying at an angle of -37.86(5)degrees to c for the P2(1)/n setting of the crystal structure. The direction of maximum expansion is approximately parallel to both [10(1) over bar] and the least-squares line passing through the projection of the chromium atoms on (010). The direction of minimum expansion lies approximately parallel to [101]. No evidence was found for either a structural or magnetic phase transition between 4.5 K and 300 K.