Low temperature structural variations and molar heat capacity of stolzite, PbWO4

The crystal structure, thermal expansion and heat capacity of PbWO4 (mineral name stolzite) scintillator material were comprehensively studied over a wide temperature range. No phase transitions were found down to 2 K (I 41/a , scheelite structure type). A distinct feature of the temperature induced structural variations in PbWO4 are the different thermal elongations of shorter and longer Pb–O distances. The low-temperature thermal expansion of PbWO4 was parameterized on the basis of the 1st order Grüneisen approximation using a Debye function for the internal energy with a Debye temperature of 237 K, a bulk modulus of 67 GPa and a Grüneisen parameter of 1.08. The expansion along the c -axis is about 2.5–3 times higher in the range 23–290 K than along the a -direction. This pronounced anisotropy of the thermal expansion arises from the arrangements of rigid tetrahedral WO42− units along 〈100〉-directions〈100〉-directions while Pb2+ cations occupy the sites between WO42− in 〈001〉-directions