Abstract
Comparison studies of the perovskite compounds system R1-xCaxMnO3 (R=La,Bi) by both Mn K-beta-emission spectroscopy and x-ray-absorption near-edge spectroscopy (XANES) are presented. The insensitivity of x-ray-emission measurements to structural distortions coupled with the sensitivity of x-ray-absorption near-edge measurements to changes in both structure and valence enable one to detect the presence of structural distortions, such as local Jahn-Teller (JT) distortions. Theoretical XANES computations fur pure cubic perovskite and locally distorted endmembers are used to show the effect of distortions on XANES spectra as well as to comment on the nature of the pre-edge features in the spectra. We show by explicit computations: that the near-edge spectra are determined by dipole transitions while pure 1s to 3d electric quadrupole transitions determine a very limited section of the pre-edge region. Simulations of the pre-edge features reveal a direct connection between local distortions and the a1 feature amplitude. The Bi-containing system is found to have significantly higher levels of distortions than the La system. XANES studies of the A MnO3 (A = La, Pr, and Nd) system reveal a direct relationship between the main line width and the magnitude of the JT distortions.