ULTRAVIOLET PHOTOREFRACTION AND THE SUPERIONIC PHASE-TRANSITION OF ALPHA-LIIO3

The photorefractive effect is investigated in nominally pure alpha-LiI O3 crystals within the 333-514.5 nm spectral range. In the temperature range of 180 K-240 K, i.e., the temperature range of the superionic p hase transition, a dramatic decrease of the diffraction efficiency by a factor 100 is observed. This can be explained by the formation of an ionic complementary grating having an activation energy for thermal e rasure of 0.32 +/-0.03 eV. Thermal fixing can be achieved by holograph ic recording at temperatures below about 180 K, developing the complem entary grating at room temperatures, and finally recovering the comple mentary grating below 180 K. In contrast to the assumptions made for t he thermal fixing process in other crystals. e.g., LiNbO3, the mobile ionic species in alpha-LiIO3 are mainly lithium ions.