Phase transitions in H-bonded deuterated Rochelle salt crystal

Structural changes in Rochelle salt on phase transitions revisited in a multi-temperature single-crystal X-ray diffraction study

“…7). Their shapes resemble the temperature dependencies of the dielectric susceptibility and spontaneous polarization reported earlier (Mueller, 1935;Cady, 1946;Stasyuk & Velychko, 2005;Guoxiang et al, 2008;Levitskii et al, 2010;Khan & Upadhyay, 2021).…”

“…The temperature dependencies of the atomic displacement parameters indicate clearly that the model of static disorder providing two positions for each atom is not valid at least for the LT-PE phase. The atomic displacement parameters of K1 do not show a critical temperature dependency similar to that of dielectric susceptibility or spontaneous polarization (Mueller, 1935;Cady, 1946;Stasyuk & Velychko, 2005;Guoxiang et al, 2008;Levitskii et al, 2010;Khan & Upadhyay, 2021). On transition from the PE to the FE phase the residual density near the K1 atom does not change much, and is similar in the FE and PE phases.…”

“…Their nature has been extensively studied since the ferroelectric properties were detected. The most popular theory relating the thermodynamics of the phase transitions with structural changes was proposed by Mitsui (1958) and developed further by different groups (Moina, 2012;Moina et al, 2011;Levitskii et al, 2009Levitskii et al, , 2008Levitskii et al, , 2010Khan & Upadhyay, 2021). This model considers two sublattices with oppositely directed dipole moments, which are thermodynamically equivalent and compensate each other's dipole moments in the paraelectric phases, becoming thermo- ISSN 2052-5206 dynamically inequivalent in the temperature range corresponding to the ferroelectric phase.…”

Halide Anions Tuning of Lead‐Free Perovskite‐Type Ferroelectric Semiconductors with Inverse High‐Temperature Symmetry Breaking

“…Interestingly, it shows a counterintuitive ITSB during the hightemperature phase transition. A well-known example of ITSB is the first ferroelectric Rochelle salt (KNaC 4 H 4 O 6 •4H 2 O), [22] whose low-temperature ferroelectric phase transition shows the ITSB. ITSB phenomena origin from above the group-subgroup relationship between the two phases with the symmetry element changes from 8 (E, C 2 , 2C 2 ″, i, 𝜎 h , 𝜎 d , 𝜎 v ) of the mesophase to 4 (E, C 2 , i, 𝜎 h ) of the HTP (Figure S6, Supporting Information).…”

“…Typically, the temperature can induce ferroic phase transitions, including ferroelasticity and ferroelectricity, which involve a shift from higher symmetries in the high-temperature phase to lower symmetries in the lowtemperature phase. However, there exist certain instances that demonstrate a counterintuitive phenomenon known as inverse temperature symmetry breaking (ITSB), [20,21] as observed in the first ferroelectric Rochelle salt [22] and ferroelastic materials [(C 2 H 5 ) 4 N][(CH 3 ) 4 N]MnBr 4 . [23] This unconventional form of symmetry-breaking presents an alternative approach to the exploration of new ferroic materials that can operate effectively at high temperatures.…”