Thermal expansion and phase transitions of sodium potassium tartrate tetrahydrate (RS)

Abstract

Lattice parameters of Rochelle salt (RS) crystals, K.Na.C4H4O6.4H2O, have been accurately determined by the Bond method with a high‐stability temperature attachment. The 2θ angles of the chosen Bragg reflections have been measured in a temperature range from 143 to 308 K. Thermal expansion coefficients have been computed from the fitting of the thermal variation of the lattice parameters to low‐order polynomials. Temperature dependence of the thermal expansion coefficients has also been investigated; anomalies connected with the ferroelectric phase transitions are much stronger than those occurring in the low‐temperature region but a low‐temperature phase transition seems very probable.

Piezoelectric Effect in Rochelle Salt

“…Unit cell volume (volume per two pseudospins from the same site and different sublattices) is v = 5.219 × 10 −22 cm 3 (Bronowska, 1981). The results of calculations made for static dielectric characteristics are shown together with experimental data in Fig.…”

Mitsui model with diagonal strains: A unified description of external pressure effect and thermal expansion of Rochelle salt NaKC_4H_4O_6·4H_2O

“…Strictly speaking, T 0 i are not the fitting parameters of the model, since the reference point can be chosen arbitrarily. At 308 K and at ambient pressure, the lattice constants are [35] The "seed" linear thermal expansion coefficients α 0 i were chosen to yield the thermal strains ε i at T C1 equal to α 275 i (T C1 − T C2 ), where α 275 i are the experimental [31] values of the expansion coefficients in the middle of the ferroelectric phase (at 275 K).…”

Ferroelectric displacement of atoms in Rochelle salt

“…In those calculations, the lattice constants by the Bronowska 15 have been used. The large relative displacements of atoms were obtained for O͑10͒, O͑3͒, O͑8͒, O͑6͒, and O͑4͒ ͑⌬Ͼ0.06 Å͒.…”