Crystal structure and second harmonic generation in Bi2TeO5: An X-N study from synchrotron and neutron diffraction data

Abstract

Bi2TeO5 has been obtained in polycrystalline form via solid state reaction and structurally characterized from both synchrotron and neutron powder diffraction data, enabling the precise determination of the atomic positions. The crystal structure is defined in the acentric Amb2 space group, containing three crystallographically unequivalent Bi atoms. The position of the stereochemically active electron lone pairs of both Bi3+ and Te4+ ions is inferred to be opposite to the strongly covalent BiO and TeO chemical bonds; the global electron polarization arises from the non-compensated Bi3+ lone electron pairs. Additionally, from difference Fourier maps between synchrotron and neutron diffraction data (X-N technique) it was possible to observe experimental evidence of the lone electron pair for Bi3+. Nonlinear optical measurements display highly active second harmonic generation response, comparable to that of reference AgGaSe2.