Combined EXAFS and first-principles theory study of Pb1-xGexTe

The narrow band-gap semiconductor Pb1-xGexTe has a low-temperature ferroele ctric rhombohedral phase whose average structure is a distorted rocksalt st ructure. We have measured the extended x-ray-absorption-fine-structure (EXA FS) spectra of Pb1-xGexTe with x approximate to 0.3 at the Ge and Te K edge s and at the Pb L-III edge. Guided by first-principles calculations, we cre ate a model for the local structure as a distortion from the ideal rocksalt structure. By corefining the spectra from these three edges, we demonstrat e that the data are consistent with our fitting model and we directly measu re several secondary structural distortions predicted by the theory. This w ork demonstrates a powerful approach to the determination of local structur es in complex materials by using first-principles calculations in conjuncti on with EXAFS measurements. [S0163-1829(99)13041-8].