Barium strontium tantalate

Earlier work on photorefractive materials was centered on the discovery of the properties of the phenomenon in optical crystals, most notably lithium niobate, strontium barium niobate, and barium tantalate. Both the mathematics of the theory of photorefraction outlined above and its application to these materials and... 

The principal materials used for pyroelectric detectors are members of the TGS group, lithium tantalate, strontium barium niobate, ceramics members of the lead zirconate titanate (PZT) group and, more recently, films of the polymers polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVFj). 

Since the electro-optic tensor has the same symmetry as the tensor of the inverse piezoelectric effect, the linear electro-optic (Pockels) effect is confined to the symmetry groups in which piezoelectricity occurs (see Table 8.3). The electro-optic coefficients of most dielectric materials are small (of the order of 10 m V ), with the notable exception of ferroelectrics such as potassium dihydrogen phosphate (KDP KH2PO4), lithium niobate (liNbOs), lithium tantalate (LiTaOs), barium sodium niobate (Ba2NaNb50i5), or strontium barium niobate (Sro.75Bao.25Nb206) (Zheludev, 1990). For example, the tensorial matrix of KDP with symmetry group 42m has the form... 

As ceramics based on multicomponent oxides, the following systems were taken into consideration calcium titanosilicate [61], strontium bismuth tantalate [62], barium magnesium tantalite [63], sodium cobalt oxide [64], and muUite [65-78]. 

For room temperature operation, a most attractive thermal detector is the pyroelectric element. It is a small capacitor with a dielectric material that possesses a temperature sensitive dipole moment. So far, the most successful dielectric is triglycine phosphate (TGS), particularly if doped with L-alanine. Its Curie point is at 49 °C and, consequently, it must be operated below that temperature. (Above the Curie point, these dielectrics lose their pyroelectric properties.) Other suitable materials include lithium tantalate and strontium barium niobate. The voltage across a capacitor of charge Q is... 

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