Compositions in the (Pb1−xBix (Ti1−xFex)O3 solid solution system for x ⋚ 0.7 show unusually large tetragonal distortion. High-temperature x-ray diffraction was used to study the tetragonal distortion as a function of temperature (25–700 °C) for compositions (x = 0–0.7) using powders prepared by solid-state reaction in the above system. Large changes in the lattice parameters were observed over a narrow temperature range near Curie temperature (TC) for compositions near the morphotropic phase boundary (MPB) (x ≃ 0.7). Compositions near MPB showed a c/a ratio of 1.18 at room temperature. Polar plots of lattice constants at different temperatures indicated strong anisotropic thermal expansion with zero thermal expansion along the [201] direction.

Grain-oriented glass-ceramics of LizSizOs, fresnoite (BazTiSizOs), and its isomorphs Sr2TiSi208 and BazTiGe2Os, were prepared by recrystallizing glasses in a temperature gradient. Electromechanical and hydrostatic piezoelectric properties of these glass-ceramics were measured. Piezoelectric voltage coefficients g , and hydrostatic voltage coefficient gh of these glass-ceramics are comparable to those of polyvinylidene fluoride and an order of magnitude higher than the corresponding values of lead zirconate-titanate. These glass-ceramics seem to be attractive candidate materials for hydrophones and several piezoelectric devices. Hydrostatic piezoelectric properties of BazTiSizOs and BazTiGeZO8 single crystals were also measured. The unusually high values of gh in fresnoite single crystals and glass-ceramics are supposed to be due to positive d3, in these materials. A composite model is proposed to explain the positive sign of d3, in fresnoite based on its crystal structure and internal Poisson's ratio stress.

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.

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