Abstract
The pressure- and temperature-dependent phase transitions in the ferroelectric material rubidium hydrogen sulfate (RbHSO4) are investigated by a combination of neutron Laue diffraction and high-pressure X-ray diffraction. The observation of disordered O-atom positions in the hydrogen sulfate anions is in agreement with previous spectroscopic measurements in the literature. Contrary to the mechanism observed in other hydrogen-bonded ferroelectric materials, H-atom positions are well defined and ordered in the paraelectric phase. Under applied pressure RbHSO4 undergoes a ferroelectric transition before transforming to a third, high-pressure phase. The symmetry of this phase is revised to the centrosymmetric space group P21/c, resulting in the suppression of ferroelectricity at high pressure.
Highlights
IntroductionFerroelectric behaviour in RbHSO4 was first reported by Pepinsky & Vedam (1960)
Rubidium hydrogen sulfate, (RbHSO4) is one member of the general family of solid-acid proton conductors, MHAO4, where M = Na+, K+, Rb+, Cs+, or NH4+ and A = S or Se
State-of-the-art thermal-neutron Laue diffractometers allow collection of extensive diffraction data to a similar precision as traditional monochromatic instruments with a gain in data collection rate of one-to-two orders of magnitude (McIntyre et al, 2006). We show that this technique enables confirmation of the ordered proton positions as well as yielding accurate O-H bond lengths which help to clarify the mechanism of ferroelectricity in rubidium hydrogen sulfate
Summary
Ferroelectric behaviour in RbHSO4 was first reported by Pepinsky & Vedam (1960). Their efforts to understand ferroelectricity in ammonium hydrogen sulfate (NH4HSO4) focused on ordering within the N-H...O hydrogen bonds. To their surprise, isomorphous RbHSO4 showed a low-temperature ferroelectric phase without the requirement of cation-anion hydrogen bonds. Further measurements have shown ferroelectric transitions to be prevalent throughout the MHAO4 family (Sinitsyn, 2010). Subsequent dielectric studies have revised the transition temperature, and recent piezoresponse force microscopy settled on the generally accepted Curie temperature of 264 K (Lilienblum et al, 2013)
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