X-ray structure refinement and pyroelectric investigation of fresnoite, Ba2TiSi2O8

Abstract

1985) X-ray structure refinement and pyroelectric investigation of fresnoite, Ba2TiSi2O8, Ferroelectrics, 62:1, 17-26, Crystal structure parameters have been refined from single crystal x-ray intensity data collected on Ba,TiSi,O, at 24 and 300°C. Anisotropic refinements in space group P4hm yielded residuals of 0.035 and 0.042 at 24 and 300°C, respectively. F'yroelectric measurements give a room temperature pyroelectric coefficient of + 10 pC m-' K-'. A structural mechanism for the pyroelectric effect is discussed in terms of large oxygen displacements. A sign reversal in the pyroelectric coefficient occurs at 160°C. perhaps caused by the cancellation of primary and secondary effects.

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

“…The bond distances and bond angles are in good agreement with the earlier report [2], although the present values are more precise. The structural refinement results given by Moore and Louisnathan [2] and Markgraf et al [9] are well matching with the present work. The single crystal data indicates that the interatomic distance Ba-O varies from 2.65 Å to 3.34 Å [9].…”

“…It was reported that an elastic anomaly observed at 435 K might likely be associated with a commensurate-incommensurate phase transition [14]. However, the single crystal X-ray data taken at 297 K and at 573 K revealed no change in symmetry except small change in atomic position, the largest of which were less than 0.02 Å [9]. 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 .…”

“…It is a rare mineral and showing noncentrosymmetric tetragonal structure of point group 4mm with space group C 2 4V -P4bm [2]. Due to the noncentrosymmetric crystal structure, this material shows good ferro, piezo, pyro as well as optical and other nonlinear properties useful for different practical devices [3][4][5][6][7][8][9][10]. The electromechanical coupling factor of single crystal grown by Czochralski method is large enough (k = 0.28) for piezoelectric devices and hence it could be exploited as an alternate substrate material for surface acoustic wave (SAW) devices [11,12].…”

In Search of Inorganic Nonlinear Optical Materials for Second Harmonic Generation

“…That such a bonding possibiliy transforming the TiO square pyramids into highly distorted TiO octahedra that are trans-connected in this structure is not unlikely is suggested by the &&undersaturation of the bond valence in the apical oxygen'' (15). Bond valence calculations (23) using the more recent structural data on fresnoite (19) give a value of 1.368 for the apical oxygen, indeed showing considerable valence undersaturation for this oxygen. The geometric orientation of the TiO square pyramids in the structures of Cs TiOP O (Fig.…”

“…7). Considering that fresnoite is a potential NLO structure (18,19), we believed that it is important to establish the role of square-pyramidal TiO toward SHG properties. In view of the foregoing, we prepared and examined several members of borates, silicates, and phosphates of the above-mentioned structure types containing NbO /TiO octahedral chains as well as isolated TiO square pyramids and examined their SHG response toward 1064-nm laser radiation.…”