Photorefractive properties of Bi 4 Ti 3 O 12

Three gratings are observed during holographic recording in ${\mathrm{Bi}}_{4}$${\mathrm{Ti}}_{3}$${\mathrm{O}}_{12}$: There is a primary photoinduced grating with fast response and a dephasing of \ensuremath{\pi}/2 with respect to the light pattern. It is compensated for by a complementary charge grating with much slower response. The third grating identified by phase-shift experiments is an absorption grating. At an intensity of about 0.5 W/${\mathrm{cm}}^{2}$, a peak refractive-index change of \ensuremath{\Delta}n=1.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ is achieved with a response time constant ${\mathrm{\ensuremath{\tau}}}_{1}$=40 ms. The mobility-lifetime product of the charges responsible for the primary grating is \ensuremath{\mu}${\mathrm{\ensuremath{\tau}}}_{\mathrm{R}1}$=7.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ ${\mathrm{cm}}^{2}$/V. The conductivity of the complementary charges is much smaller than that of the primary charges, which makes it possible to prolong the readout time of the recorded holographic grating considerably.