LOW-TEMPERATURE PHASE-TRANSITIONS IN SOME QUATERNARY SOLID-SOLUTIONS OF IV-VI SEMICONDUCTORS

Samples of PbSxSeTe1-x-y, Pb1-xSnxTe1-ySey and Pb1-xSnxTe1-ySy quatern ary solid solutions were investigated in the 4-200 K temperature range using electrical and X-ray methods. The regions where low-temperature phase transitions take place were established. It is shown that phase transitions in these solid solutions are associated with off-center S and Sn ions. The dependence of the phase transition temperature on th e composition of solid solutions can be qualitatively described taking into account the influence of substitutional disorder on ordering and tunneling of off-center ions.