Electron paramagnetic resonance (EPR) has been used to identify the primary electron and hole traps responsible for ‘‘gray tracks’’ in flux-grown KTiOPO4(KTP). Ionizing radiation (x rays) was used to produce the gray-track effect. During an irradiation at 0 °C, a broad absorption band peaking near 500 nm is introduced, the EPR spectra from a series of Ti3+ centers appear, and the dominant EPR spectrum associated with Fe3+ ions decreases significantly. Following the irradiation, the decay of the optical absorption and the Ti3+ centers, along with the growth of Fe3+ centers, were monitored over a period of 20 h at room temperature. Changes in the EPR spectra of the Ti3+ and Fe3+ centers during the anneal correlated with the decay of the induced optical absorption (i.e., gray track). These results demonstrate that Fe3+ centers are the primary hole trap and Ti4+-VO complexes are the primary electron trap responsible for gray track formation in flux-grown KTP crystals.

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The electrostrictive behavior in single crystals of Pb(MglpNb2/3)03 (PMN) and 0.93Pb(Mg1!3 NbZ/3)03 -0.07PbTi03(PMN-7%PT) was investigated as a function of crystallographic direction. The pseudocubic nature of these materials became highly anisotropic at relatively high electric fields. The observed anisotropy was believed to be associated with an electric field induced rhombohedra1 symmetry. Strain values were found to be larger for (001 ) oriented crystals though larger polarization values were measured in (1 11) oriented crystals, a consequence of larger electrostrictive coefficients (Q,). The electrostrictive coefficient Q, of the induced phase was found to be independent of composition. Though the crystals exhibited a high degree of anisotropy, no apparent improvement in induced polarization or strain was found when compared with polycrystalline counterparts.

Electron paramagnetic resonance ͑EPR͒ has been used to characterize a new hole trap in flux-grown KTiOPO 4 crystals. This center is formed at room temperature when the crystals are exposed to either 60 kV x rays or a pulsed 355 nm laser beam. Principal g values measured at room temperature are 2.0030, 2.0102, and 2.0320. The intensity of the EPR spectrum is considerably larger in a silicon-doped sample, thus suggesting that the responsible defect consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. Also, a broad optical absorption band peaking near 500 nm has been observed in the irradiated samples. The silicon-associated hole centers thermally decay over a period of several days at room temperature as electrons are released from Ti 3ϩ traps. Analysis of hole-center decay curves obtained at three temperatures ͑291, 300, and 311 K͒ has shown that the kinetics of this electron-release process are primarily second order. The activation energy is approximately 0.80 eV and the ''frequency'' factor is approximately 4.1ϫ10 9 s Ϫ1 .