NIR absorption of Nb₄₊ polarons in reduced SBN crystals

Abstract

A broad absorption band around 0·72 eV, assigned to the absorption of Nb₄₊ polarons, is observed, even at room temperature and above, in pure SBN, SBN:Cr or SBN:Ce crystals after previous reduction treatment at T>800°C in Ar, vacuum or H₂. The absorption spectrum of Nb₄₊ polarons in reduced SBN crystals shows a considerable dichroism, which exists even far above room temperature. The spectral shape of the Nb₄₊polaron absorption shifts to higher energies with decreasing temperature. The concentration of polarons can be estimated from the magnetic susceptibility[1] and yields a value of the optical oscillator strength f = 5 × 10⁻² for the NIR-absorption.