A Neutron Powder Diffraction Determination of the Thermal Expansion Tensor of Crocoite (Pbcro4) between 60 K and 290 K

Kevin S. Knight
ISIS Science Division, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OXI 1 0QX UK

Abstract: 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 ≤ T ≤ 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 α11 = 33.1(1) × 10−6K−1, α22 = 15.72(3) × 10−6K−1, α33 = 3.36(1) × 10−6K−1, with α22 parallel to b and α11 lying at an angle of −37.86(5)° to c for the P21/n setting of the crystal structure. The direction of maximum expansion is approximately parallel to both [101¯] 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.

Keywords: crocoite • thermal expansivity • neutron diffraction • PbCrO4

Mineralogical Magazine; December 1996 v. 60; no. 403; p. 963-972; DOI: 10.1180/minmag.1996.060.403.11
© 1996, The Mineralogical Society
Mineralogical Society (www.minersoc.org)