Low-temperature elastic and dielectric properties of K3Na(SO4)2 crystals

Abstract

Elastic and dielectric properties of glaserite K 3 Na(SO 4 ) 2 single crystal were examined using the method of composite oscillators, Brillouin light scattering methods and dielectric spectroscopy. Measurements were performed in the temperature range from 18 K to 300 K. Anomalies in the temperature dependencies of Brillouin shift and dielectric permittivity at about 70 K confirmed the earlier predicted phase transition at 75 ± 25 K. Temperature dependences of the resonance frequency of the vibrating composite oscillator, Brillouin shift measured in the [110] direction, components of dielectric permittivity tensor reveal an anomaly at about 50 K. Moreover, thermal hysteresis of the dielectric permittivity suggested the presence of an incommensurate state between T 1 = 50 K and T 2 = 70 K.

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“…Based on these results, the difference between the 23 Na nuclei with distinct local environments is responsible for the difference in 23 Na T values between the two crystals; the KNaSO 4 crystals include two types of Na + ions, whereas the K 3 Na(SO 4 ) 2 crystals contain only one type. In addition, the sulfate tetrahedra surrounding the Na nuclei are substantially distorted in KNaSO 4 crystals but are only slightly distorted in K 3 Na(SO 4 ) 2 crystals 2, 3.…”

“…The parameters of the hexagonal unit cell of KNaSO 4 are a = 5.6066 Å and c = 7.177 Å 3, and those of K 3 Na(SO 4 ) 2 are a = 5.6801 Å and c = 7.309 Å 3. There are two formula units in the KNaSO 4 unit cell but only one in the K 3 Na(SO 4 ) 2 unit cell 2, indicating the existence of two SO 4 units in the primitive cell of each type of crystal. Comparison of the trigonal structures of the KNaSO 4 and K 3 Na(SO 4 ) 2 crystals, shown in Fig.…”

DC conductivity studies in K3Na(SeO4)2 single crystals

“…It undergoes successive structural phase transition above the room temperature: the melting point at 1170 K, two high temperature phase transitions at 758 K and 730 K and low temperature phase transitions at 346 K and 333 K [2,3]. Experimental studies of these materials show that K 3 Na(SO 4 ) 2 , K 3 Na(CrO 4 ) 2 and K 3 Na(SeO 4 ) 2 undergo ferroelastic phase transitions from a point group 3m1 to 2/m at about 70 K, 239 K and at 346 K, respectively [2,4,5]. Fabry et al [6] have studied the crystal structure at both phases of KNSe.…”

Raman processes of KNaSO4 and K3Na(SO4)2 single crystals studied by 23Na and 39K nuclear magnetic resonance

“…Potassium sodium sulfate, KNaSO 4 , and tripotassium sodium sulfate, K 3 Na(SO 4 ) 2 are members of a family that can be described by the chemical formula ACBX 4 or A 3 C(BX 4 ) 2 , where A, C = Li, Na, K, Rb, Cs and BX 4 = SO 4 , SeO 4 , CrO 4 , MoO 4 1. KNaSO 4 and K 3 Na(SO 4 ) 2 single crystals both have trigonal structures, and their space groups are P3m1 and P$\bar 3$ m1, respectively 2. The parameters of the hexagonal unit cell of KNaSO 4 are a = 5.6066 Å and c = 7.177 Å 3, and those of K 3 Na(SO 4 ) 2 are a = 5.6801 Å and c = 7.309 Å 3.…”

“…Recently, Wiesner and coworkers 2, 5 reported on the low‐temperature elastic and dielectric properties of K 3 Na(SO 4 ) 2 crystals, and discussed critical phenomena observed close to 50 and 70 K. In other studies, the twin domains of the two crystals have been examined by X‐ray diffraction and electron paramagnetic resonance (EPR) 6, 7. Additionally, electrical conductivity measurements performed on pure and doped KNaSO 4 and K 3 Na(SO 4 ) 2 revealed high ionic conductivity values in the high‐temperature phase 8.…”