Fresnoite: A new ferroelectric mineral

Abstract

Fresnoite, Ba2TiOSi2O7, has been predicted structurally to be a new ferroelectric. Detection of both ac and dc dielectric hysteresis verifies the prediction. The spontaneous polarization Ps estimated from the hysteresis at 1.2 MV m−1 ac is ∼0.2 C m−2 at 295 K, comparable with the minimum Ps observed in one-dimensional ferroelectrics. A reproducible calorimetric anomaly with entropy change 0.19(3) J mol−1 K−1 at 433(2) K in polycrystalline material coincides with a small dielectric and pyroelectric anomaly previously reported in single crystals; an entropy change ∼0.2 J mol−1 K−1 at 810(5) K also accompanies a dielectric anomaly observable in ceramic samples at 805(5) K. Both calorimetric anomalies are ∼60 K wide. Observation of dielectric hysteresis at 875 K shows that neither anomaly corresponds to the Curie temperature; both are likely associated with small changes in atomic position, not with symmetry changes. Melting onset in fresnoite is 1703(1) K with undercooling as deep as 435 K.

Effect of Heat-Treatment Temperature on Optical Properties of Ba2TiSi2O8 Nanocrystallized Glasses

“…16 In addition, Takahashi et al reported that the fresnoite-type phases showed large second-order optical nonlinearities comparable to that of LiNbO 3 single crystal.…”

Preparation and Electrical Properties of Ba2TiOSi2−xGexO7 (x=0.0 and 0.2) Ferroelectric Ceramics

“…It is surprising that the ceramic samples fail to reveal the dielectric anomaly shown in case of single crystal at 433 K [3]. Not only that, but a small reproducible dielectric anomaly has also been reported in the frequency range 0.1-100 kHz at 805 K. However, the single crystal X-ray data taken at 297 K and 573 K revealed no change in symmetry except small changes in atomic position, the largest of which were less than 0.02Å [8]. Recent studies on oriented crystallization using thermal gradient, crystallization kinetics, and electrical properties through impedance spectroscopy were also carried out on fresnoite and fresnoite like glassy materials [9][10][11].…”

“…The mineral shows a noncentrosymmetric tetragonal crystal structure with space group P4bm [2]. Due to its noncentrosymmetricity, the material shows good ferroelectric, piezoelectric, pyroelectric, optical, and other physical properties useful for different practical devices [3][4][5][6][7][8]. The single crystal data of fresnoite shows a broad peak in dielectric permittivity at ∼433 K but the same peak is absent in dielectric loss curve.…”

Synthesis of Ba2TiOSi2O7 and Ba2TiOSi1.8Ge0.2O7 ferroelectric ceramics and the structure determination by Rietveld analysis

“…It has also been reported that the differential scanning calorimetry (DSC) measurement from 300 to 875 K showed a wide ($60 K) reproducible thermal anomaly at 433 K with enthalpy change DH = 60(10) J mol À1 and corresponding entropy change DS = 0.19137 J mol À1 K À1 . A thermal anomaly of comparable width was also observed at 810(5) K with DH = 160 J mol À1 and DS = 0.2 J mol À1 K À1 [13]. Uchida et al suggested that the second order optical nonlinearity of the crystal was strongly affected by the distortion of the crystal structure [15].…”

“…It is surprising that the ceramic samples fail to reveal a reproducible dielectric anomaly at 433 K shown in case of single crystal [4]. Not only that a small reproducible dielectric anomaly has also been reported in the frequency range 0.1-100 kHz at 805 K [13]. It was reported that an elastic anomaly observed at 435 K might likely be associated with a commensurate-incommensurate phase transition [14].…”