Structural and X-ray spectroscopy studies of Pb1-xBax(NO3)2 solid solutions

Abstract

Pb0.75(3)Ba0.25(3)(NO3)2, Pb0.68(3)Ba0.32(3)(NO3)2, Ba0.58(3)Pb0.42(3)(NO3)2, Ba0.81(3)Pb0.19(3)(NO3)2 crystals were grown for the first time when studying the Pb(NO3)2–Ba(NO3)2–H2O system. The crystals were grown in water solution with different relation of Pb(NO3)2 and Ba(NO3)2. It was found that series of solid solutions were formed by interaction of simple Pb(NO3)2 and Ba(NO3)2 compounds with a slow increase of volume and cell parameters from pure lead nitrate to pure barium nitrate. The crystal structure of all obtained Pb1-xBax(NO3)2 crystals belong to a cubic space group Pa-3. In these structures, Pb and Ba cations have the same coordination number 12, but different ionic radii (1.49 and 1.61 Å, respectively), anionic group is an equilateral triangle with O–O–O angle of 60° and O–O bond lengths ranging from 2.1305(8) to 2.2585(7) Å. The Pb2+ ion has a lone pair of electrons that are likely to be stereochemically active in these solid solutions leading to a significant amount of local disorder which explains the spread in the lattice parameters. The Pb1-xBax(NO3)2 solid solutions were characterized by X-ray photoelectron spectroscopy (XPS) by measuring the binding energies of the core-levels of constituting atoms and the shapes of the valence band. The XPS measurements indicate that the substitution of Pb for Ba does not cause changes in the charge states of the atoms constituting the Pb1-xBax(NO3)2 crystals. Matching the XPS valence-band spectra and the X-ray emission O Kα bands on a common energy scale indicates that the principal contributions of O 2p states occur at the top of the valence band of the crystals under study with also their substantial input in the upper and central portions of the band.