Dielectric and ultrasonic investigation of phase transition in cuinp₂s₆crystals

Broadband dielectric spectroscopy of CuInP2Se6 crystals

“…The temperature behaviour of the dielectric dispersion of CuInP 2 Se 6 crystals with a small admixture of sulphur (Fig. 2) is very similar to the dielectric dispersion of pure CuInP 2 Se 6 crystals [9]. At higher temperatures (T >> T c ) the dielectric dispersion reveals in 10 8 -10 10 Hz frequency range.…”

“…However, the calorimetric investigations showed only a broad phase transition between 220 and 240 K in this compound [8]. More accurate broadband dielectric investigations showed only nearly second order phase transition at T c =226 K [9]. From a single-crystal X-ray diffraction study follows that the high-and low-temperature structures of CuInP 2 Se 6 (trigonal space group P-31c and P31c, respectively) are very similar to those of CuInP 2 S 6 in the paraelectric and ferrielectric phases, with the Cu I off-centering shift being smaller in the former than in the latter [3,8].…”

“…11. A small amount of selenium changes dielectric properties of CuInP 2 S 6 crystals significantly: the temperature of the main dielectric anomaly shift from about 315 to 289 K, the maximum value of the dielectric permittivity ε ′ significantly decreases from about 180 to 40 (at 1 MHz), at higher frequencies (from about 10 MHz) the peak of dielectric permittivity becomes frequency-dependent in CuInP 2 (S 0.98 Se 0.02 ) 6 crystals and a critical slowing down disappears [6]. An additional dielectric dispersion appears at low frequencies and at low temperatures.…”

“…It was suggested that a coupling between P 2 S 6 deformation modes and Cu I vibrations enables the copper ion hopping motions that lead to the loss of polarity and the onset of ionic conductivity in this material at higher temperatures [4]. The investigation of ionic conductivity in CuInP 2 S 6 [5,6] have showed that σ DC follows the Arrhenius law with the activation energy E A = 0.73 eV [5] and more detailed investigations showed E A =0.635 eV [6].…”

“…Preliminary dielectric investigations of CuInP 2 (S x Se 1−x ) 6 crystals are presented in [11,12]. The data in [11] is measured only at frequency 10 kHz and the paper [12] contain data only on one compound -CuInP 2 (S 0.7 Se 0.3 ) 6 .…”