Heat treatment of cubic YbZrF7, after quenching from 1000 °C, leads to a material displaying precisely zero thermal expansion at ∼300 K and negative thermal expansion at lower temperatures. The zero thermal expansion is associated with a minimum in the lattice constant at ∼300 K. X-ray total scattering measurements are consistent with a previously proposed model in which the incorporation of interstitial fluoride into the ReO3-related structure leads to both edge and corner sharing coordination polyhedra. The temperature dependence of the experimental pair correlation functions suggests that the expansions of edge and corner sharing links partly compensate for one another, supporting the hypothesis that the deliberate incorporation of excess fluoride into ReO3 structure materials can be used as a design strategy for controlling thermal expansion. Cubic YbZrF7 has a bulk modulus, K 0, of 55.4(7) GPa and displays pronounced pressure-induced softening [K 0′ = −27.7(6)] prior to an abrupt amorphization on compression above 0.95 GPa. The resulting glass shows a single sharp scattering maximum at Q ∼ 1.6 Å–1.

Herein we report a cryogenic-temperature study on the evolution of ferroelectric properties of epitaxial Hf0.5Zr0.5O2 thin films on silicon. Wake-up, endurance, and fatigue of these films are found to be intricately correlated, strongly hysteretic, and dependent on available thermal energy. Field-dependent measurements reveal a decrease in polarization with temperature, which has been determined not to be an intrinsic change of the material property, rather, a demonstration of the increase in the coercive bias of the material. Our findings suggest that a deficiency in thermal energy suppresses the mobility of defects presumed to be oxygen vacancies during wake-up and trapped injected charge during fatigue, which is responsible for polarization evolution during cycling. This permits accelerated wake-up and fatigue effects at high temperatures where thermal energy is abundant but delays these effects at cryogenic temperatures.

Herein, we examine the influence of controllable polarization reversal and built-in electric fields on pyroelectric and electrocaloric effects in a BaTiO3 thin film using a modified indirect method. We find that the magnitude of the sample's change in polarization with temperature is sensitive to the degree of polarization reversal. The pyroelectric response is small at low fractions of switched polarization and grows larger by several factors as larger fractions of polarization are reversed. This polarization reversal-sensitive pyroelectric behavior is the result of an internal built-in field, which has the effect of destabilizing low fractions of switched polarization and producing diminished pyroelectric effect. Greater fractions of switched polarization are more stable against backswitching and permit a larger pyroelectric response. Our findings highlight a characterization method for polarization-dependent pyroelectric effects in ferroelectric thin films, where built-in field effects are also present.