Dielectric properties of KH2PO4, BaTiO3, PbZr0.65Ti0.35O3 and TlCl between 0.015 and 10 K

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Abstract
The small-signal ac permittivities (ε) of single crystal samples of KDP, BaTiO3, and TlCl, and of a ceramic sample of PZT 65/35 have been measured as a function of temperature between 0.015 and 10 K. For KDP and PZT 65/35, ε increases essentially linearly with temperature in this range, with d In ε/dT = 0.95 ± 0.15 × 10-3 K-1 and 1.81 ± 0.02 × 10-3 K-1, respectively. For BaTiO3 linear behavior is observed only between 1.5 and 4.5 K, with d In ε/dT = 9.4 × 10-4 K-1. PZT 65/35 exhibits positive deviation from this apparent linear behavior between 0.1 and 1.5 K, while BaTiO3 shows a negative deviation in this range. Both PZT 65/35 and BaTiO3 have a minimum in ε below 0.1 K and an associated change in the dielectric loss factor that depends on the frequency and amplitude of the ac signal. No temperature dependence of ε was observed below 3 K for TlCl. Potential applications of these materials at low temperatures are discussed.