Pyroelectric Coefficient of Lithium Sulfate Monohydrate (4.2-320°K)

Abstract

The pyroelectric coefficient (at constant stress) of lithium sulfate monohydrate was measured over the temperature range 4.2-320°K, in order to resolve a discrepancy between the results of Ackermann and those of Gladkii and Zheludev, and to extend the data to below 88°K. The pyroelectric coefficient was observed to change sign at 106°K in agreement with the results of Gladkii and Zheludev. The coefficient passed through a broad extremum at 50 °K and approached zero at 4.2 °K. The primary and secondary pyroelectric coefficients were calculated over the temperature range; their cancellation at 106 °K causes the sign change in the pyroelectric coefficient at constant stress. The secondary coefficient is positive at all temperatures, but the primary coefficient changes sign at 158 °K. The Born lattice-dynamical theory of the primary pyroelectric effect was extended to include contributions due both to the acoustical and to the optical spectra of a material. A Debye temperature and five Einstein temperatures calculated from heat-capacity data were used to derive an analytical expression for the primary pyroelectric coefficient.