A. Halliyal

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

Crystal structure parameters have been refined from single crystal x-ray intensity data collected on Ba2TiSi2O8 at 24 and 300°C. Anisotropic refinements in space group P4bm yielded residuals of 0.035 and 0.042 at 24 and 300°C, respectively. Pyroelectric measurements give a room temperature pyroelcctric coefficient of + 10 μC m -2 K -1. A structural mechanism for the pyroelectric effect is discussed in terms of large oxygen displacements. A sign reversal in the pyroeleetric coefficient occurs at 160°C, perhaps caused by the cancellation of primary and secondary effects.

Ba2TiGe2O8 and Ba2TiSi2O8 pyroelectric glass-ceramics

Pyroelectric glass-ceramics of composition Ba2TiGe2O8 and Ba2TiSi2O8 were prepred by crystallizing the glasses in a temperature gradient. High pyroelectric responses up to 50% of the single-crystal values were observed because of the high degree of orientation of the crystallites in the glass-ceramic samples. The piezoelectric and dielectric properties of the glasses and the glass-ceramics are also consistent with the properties of the single crystals.

Unusual pyroelectric and piezoelectric properties of fresnoite (Ba2TiSi2O8) single crystal and polar glass-ceramics

The dielectric, piezoelectric and pyroelectric properties of fresnoite (Ba2TiSi2Os) single crystal and polar glass-ceramics were studied in the temperature range - 150 to 200°C. The sign of pyroelectric coefficient is positive at room temperature and becomes negative at 190°C. The dielectric constant, pyroelectric coefficient and planar coupling coefficient show a maximum value at 160°C and the frequency constant shows a minimum at the same temperature. The probable reasons for the anomaly in these properties are discussed.

Polar glass ceramics — A new family of electroceramic materials: Tailoring the piezoelectric and pyroelectric properties

Abstract Grain oriented multicomponent polar glass-ceramics have been prepared by crystallizing the glasses in a temperature gradient. Inexpensive, large area piezoelectric and pyroelectric devices can be fabricated by this method, and by adjusting the composition of the glasses and crystallization conditions, it is possible to tailor the properties to meet device requirements. Based on the growth characteristics and the connectivity pattern of the crystallites, the piezoelectric, pyroelectric and dielectric properties of glass-ceramic composites can be predicted. Two examples discussed in this paper are piezoelectric glass-ceramics which are not pyroelectric, and pyroelectric glass-ceramics which are not piezoelectric.

Study of the piezoelectric properties of Ba2Ge2TiO8 glass-ceramic and single crystals

Glass-ceramics of composition Ba2Ge2TiO8 with oriented crystallites were prepared by crystallizing the glasses in a temperature gradient. The degree of preferred orientation of the crystallites as a function of depth was studied. Piezoelectric resonance properties of both the glass-ceramics and the single crystals were studied. The piezoelectricd33 coefficient, the frequency constants and the electromechanical coupling coefficients of the glass-ceramic were comparable to the single-crystal values.

Phase transitions, dielectric, piezoelectric and pyroelectric properties of barium titanium germanate Ba2TiGe2O8 single crystals

Measurement of the dielectric permittivity e33, the pyroelectric coefficient p3 and the piezoelectric planar coupling kp and frequency constant Np in single crystal Ba2TiGe2O8 show clear evidence of a heretofore unobserved first order phase change which occurs at - 50°C on cooling and near 0°C on heating. The balance of evidence suggests that the transition is to a reorientable but irreversible ferroelectric phase, involving a tilt of the prototypic polar c axis. The inversion of the sign of the pyroelectric effect reported earlier near 135°C is confirmed and is attributed to the changing balance between primary and secondary components in the pyroelectric coefficient.

Dielectric, piezoelectric and pyroelectric properties of Sr2TiSi2O8 polar glass-ceramic: A new polar material

Polar Sr2TiSi2O8 glass-ceramics were prepared by recrystallizing glasses in a steep temperature gradient. The dielectric, piezoelectric and pyroelectric properties were studied as a function of temperature in the temperature range −150 to 200‡ C. The sign of the pyroelectric coefficient is positive at room temperature and is attributed to the dominance of the secondary pyroelectric effect over the primary effect. Anomalies were observed in the dielectric, pyroelectric and piezoelectric properties and a large hysteresis was observed in all these properties. Probable causes for the anomalies are discussed.

Piezoelectric properties of lithium borosilicate glass ceramics

Glass ceramics in the system Li2O‐SiO2‐B2O3 with oriented crystallites were prepared by crystallizing the glasses in a temperature gradient. Piezoelectric and electromechanical properties of the glass ceramics are reported. Some of the compositions exhibit low temperature coefficient of resonance, comparable to LiTaO3 single crystals. Advantages of fabricating glass‐ceramic piezoelectric resonators are described and the possibility of using them in surface acoustic wave (SAW) devices is suggested.

Grain oriented glass-ceramics: New materials for hydrophone applications

Abstract Grain oriented glass-ceramics of fresnoite (Ba2TiSi2O8) and its modifications Sr2TiSi2O8 and Ba2TiGe2O8 have been prepared by recrystallizing glasses in a temperature gradient. Piezoelectric voltage coefficients g33 and hydrostatic voltage coefficient gh of these glass-ceramics are comparable to those of PVF2 and an order of magnitude higher than the corresponding values of PZT. These glass-ceramics seem to be attractive candidate materials for hydrophones and several piezoelectric devices. Hydrostatic piezoelectric properties of Ba2TiSi2O8 and Ba2TiGe2O8 single crystals are also reported.

Thermal expansion of ceramics in Pb(Zn13Nb23)O3 - based solid solution systems

Abstract No systematic study on the thermal expansion behavior of Pb(Zn 1 3 Nb 2 3 ) O 3 - based ceramics has been made so far. This study is very important because these materials are potential candidates for multilayer capacitors and optical-mirrors substrates.Lead-zinc-niobate Pb(Zn 1 3 Nb 2 3 ) O 3 (PZN) based ceramics with perovskite structure are difficult to synthesize because of the formation of a undesirable pyrochlore phase. However, an addition of BaTiO 3 , PbTiO 3 or SrTiO 3 stabilizes perovskite structure in PZN. In this work ceramic samples in the solid solution systems of PZN with these additives were prepared and thermal expansion measurements were carried out on the ceramic specimens using a push rod dilatometer. No substantial and systematic change in bulk thermal expansion with the change in composition was observed. Most of the samples demonstrated very low thermal expansion at lower temperature.