X-Ray Natural Circular Dichroism in Langasite Crystal at the Ga and La Edges

Resumo

X-ray natural circular dichroism (XNCD) and its structural nature have been investigated in a langasite (La₃Ga₅SiO₁₄) crystal at an incident radiation energy close to the Ga K-absorption edge and the La L_2,3-absorption edges. An XNCD signal was observed mainly beyond the absorption edge, which confirmed the existence of delocalized mixed p–d electronic states in Ga and d–f and d–p electronic states in La. Calculations with application of the multiple scattering method have made it possible to separate the contributions from three crystallographically nonequivalent Ga sites to the absorption spectrum and the XNCD signal and explain adequately the largest contribution of the Ga atom occupying the 1a site to the XNCD signal.