Study of the intrinsic absorption edge of layered molybdates exhibiting low-temperature phase transitions

The intrinsic absorption edge of (AE) of layered single crystals of CsR(MoO4)2 where R is the ion of a rare-earth element or bismuth, is studied at room temperature. A correlation is found between the dependence of the gap width and the dependence of the melting temperature on the interlayer parameter a for a series of these compounds. For single crystals in the system CsDy(Mg1−x Wx O4)2 with x = 0, 0.02, 0.05, 0.1, and 0.2, which undergo first-order low-temperature transitions, the AE is studied above and below the transition temperatures Tc; the mechanism of the phase transition (PT) in CsDy(MoO4)2 has not been finally established. The study performed showed that the interband electron–phonon interaction cannot be the microscopic mechanism for the PT in CsDy(MoO4)2 jumps in the AE, whose magnitude drops as the tungsten concentration CW is increased, while Tc increases, were observed at the PT temperatures. Extrapolarization of the jumps in AE to zero permits obtaining critical values of Tc and CW with which first-order transitions become second-order PT (tricritical point). The energy kTc at this point determines the magnitude of the interaction force leading to the PT. The magnitude of this energy is close to the energy of the change in the interlayer atomic interaction in the compounds studied.

Hali tarjima qilinmagan