Synthesis of a mixed‐valent europium(II, III)‐borate and its optical and magnetic behavior

Abstract

The mixed‐valent, europium borate Eu5(BO3)4 was synthesized from Eu2B2O5 and EuB2O4. Its structure was refined by Rietveld analysis. Eu5(BO3)4 crystallizes in space group Pnma (a=2229.77(2) pm, b=1599.91(2) pm, and c=877.75(1) pm) and was found to be isostructural with Eu5(BO2.51N0.49)4. Powder reflectance spectra (UV/vis/NIR) and magnetic susceptibility data of Eu5(BO3)4 and of the reference compounds EuIIB4O7 and EuIIIBO3 were measured. The spectrum of the mixed‐valent europium(II, III) borate shows the 7F0→7F6 transition of the Eu3+ ion and the intervalence charge transfer Eu2+→Eu3+. The experimental Bohr magneton number of Eu5(BO3)4, μobs/μB=14.90, agrees well to μcalc/μB for a combination of three Eu2+ and two Eu3+ per formula.