Temperature dependence of the Pd [ital K]-edge extended x-ray-absorption fine structure of PdC[sub [ital x]] ([ital x][similar to]0. 13)

Pd [ital K]-edge extended x-ray-absorption fine-structure (EXAFS) and x-ray-absorption near-edge-structure (XANES) measurements were performed on a Pd carbide phase, PdC[sub [ital x]] (with [ital x][similar to]0.13), and metallic Pd powder at temperatures between 40 and 423 K. The data were analyzed by nonlinear least-squares fitting using an [ital ab] [ital initio] theoretical standard. The average lattice expansion of the carbide phase, 2.7[plus minus]0.1% relative to Pd metal, agrees well with previous x-ray- and neutron-diffraction results. The temperature dependence of the Pd-Pd nearest-neighbor mean-squared relative displacement ([sigma][sup 2]) yields a Debye temperature, [Theta][sub [ital D]]=295[plus minus]10 K for Pd powder. There is an additional static-disorder contribution in [sigma][sup 2] of 0.0009[plus minus]0.0002 A[sup 2], relative to bulk Pd metal. The Debye temperature of PdC[sub 0.13] powder is also 295[plus minus]10 K. There is, however, an additional static-disorder contribution to [sigma][sup 2] of 0.0012 A[sup 2], relative to Pd powder, probably the result of local distortion of the Pd lattice by interstitial C. The Pd-C coordination is not directly observed in a Fourier transform of the EXAFS. The location of C in octahedral interstices is evident by its effect, through multiple scattering, on the magnitude of the second Pd-Pd peak in the Fourier transform magnitude of the EXAFS data, which is greatly reduced. The Pd [ital K]-edge XANES spectrum of PdC[sub 0.13] is nearly identical to that of Pd metal. There is no significant chemical shift ([le]0.5 eV) of the Pd [ital K] edge of PdC[sub [similar to]0.13].