Abstract
LaOCl doped with 0–10 mol% Cr was synthesized by thermal decomposition of chlorides. X-ray diffraction (XRD) analysis revealed that incorporation of chromium results in a decrease of the lattice parameter a and a simultaneous increase of the lattice parameter c. The local structure of chromium ions was studied with X-ray photoelectron (XPS), X-ray absorption (XANES), multifrequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy techniques. It was determined that synthesis in oxidizing atmosphere promotes the incorporation of chromium ions predominantly in the 5+ oxidation state. Changes of chromium oxidation state and local environment occur after a subsequent treatment in reducing atmosphere. Spin-Hamiltonian (SH) parameters for a Cr5+ and two types of Cr3+ centers in LaOCl were determined from the EPR spectra simulations.
Highlights
Introduction of Chromium Ions in LaOClLanthanum oxychloride (LaOCl), which is being considered for a variety of applications including gas sensors [1,2,3,4,5,6,7,8], catalysts [9,10,11], and solid electrolytes [12,13,14], is one of the most widely investigated compounds from the class of lanthanide oxyhalides
Due to the smaller ionic radius of Cr3+ (0.615 Å) in comparison to La3+ (1.032 Å) [56], a contraction of the LaOCl lattice resulting in a decrease of the lattice parameters a and c is expected
The oxidation state and local environment of chromium ions were studied in LaOCl samples synthesized in different annealing atmospheres
Summary
Gradual changes of lattice parameters with an increase of Cr content were detected (see Figure 3), suggesting the incorporation of Cr ions in the LaOCl lattice. In the case of isovalent substitution, Cr3+ ions are expected to incorporate in La3+ positions. Due to the smaller ionic radius of Cr3+ (0.615 Å) in comparison to La3+ (1.032 Å) [56], a contraction of the LaOCl lattice resulting in a decrease of the lattice parameters a and c is expected. Gradual changes of lattice parameters with an increase of Cr content were (see Figure 3), suggesting the incorporation of Cr ions in the LaOCl lattice. Cr3+ ions are expected to incorporate in La3+ positions. LaOClsamples samples withdifferent different concentrations ofCr. the LaOCl lattice resulting in a with decrease ofconcentrations the lattice ofparameters a and c is expec
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