Аннотация:The first study of some thermodynamic properties of a Cs2HfCl6 (CHC) scintillating crystal has beenperformed in a wide temperature range of 5–300 K. The CHC crystal exhibits a high thermal expansioncoefficient (5.17 105 at 171 K), along with an extremely low heat conductivity (1.710 W m1 K1 at50 K). A high heat capacity (1.22 J kg1 K1 at 3.8 K) along with a drastically low free mean path for phonons(about 26 Å) at temperatures around 50 K makes the CHC crystal unsuitable as a target materialfor cryogenic detectors. The results of the first operation of the CHC crystal as a cryogenic detector atsub-Kelvin temperatures clearly show the unfavorable phonon propagation properties of the material.On the other hand, the CHC crystal demonstrates excellent scintillating characteristics with a relativelyhigh light yield under gamma irradiation (the detected signal is about 5200 photons per MeV). Therefractive index within the (1.66–1.67) interval for light in visible and near-infrared spectral ranges wasmeasured at room temperature. A cost- and time-effective approach for new crystalline materialcharacterization as a target for cryogenic detectors based on the evaluation of the thermodynamicproperties of the material is proposed