Valence transitions in negative thermal expansion material SrCu₃Fe₄O₁₂.

The valence states of a negative thermal expansion material, SrCu3Fe4O12, are investigated by X-ray absorption and (57)Fe Mössbauer spectroscopy. Spectroscopic analyses reveal that the appropriate ionic model of this compound at room temperature is Sr(2+)Cu(~2.4+)3Fe(~3.

Pd(2+)-incorporated perovskite CaPd3B4O12 (B = Ti, V).

Novel A-site ordered perovskites CaPd(3)Ti(4)O(12) and CaPd(3)V(4)O(12) were synthesized under high-pressure and high-temperature of 15 GPa and 1000 °C. These compounds are the first example in which a crystallographic site in a perovskite-type structure is occupied by Pd(2+) ions with a 4d(8) low spin configuration. The ionic models for these compounds were determined to be Ca(2+)Pd(2+)(3)Ti(4+)(4)O(12) and Ca(2+)Pd(2+)(3)V(4+)(4)O(12) by structural refinement using synchrotron X-ray powder diffraction, hard X-ray photoemission, and soft X-ray absorption spectroscopy.