X-ray studies of off-center ions and ferroelectricity in PbSxTe1-x and ZnxCd1-xTe alloys

Using X-ray Absorption Fine Structure (XAFS) and x-ray diffraction, we have investigated the local structure of disordered PbSxTe1-x and ZnxCd1-xTe alloys at temperatures below and above the reported ferroelectric transition temperatures. For the PbSxTe1-x alloys (x = 0.10, 0.18, and 0.30), the sulfur ions are found to be displaced from the site center in both the high and the low temperature phases. Below the transition temperature, the Pb and Te sublattices are observed to shift relative to one another, characteristic of a displacive transition. For ZnxCd1-xTe alloys (x = 0.10 and 0.20), no relative shift between the cation and anion sublattice is observed within experimental uncertainty. If the Zn ions are off center in this system, the maximum displacement is approximately 0.04 Å.

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Physics Department, North Carolina State University, Raleigh, NC