NIR absorption of Nb4+ polarons in reduced SBN crystals

A broad absorption band around 0.72 eV, assigned to the absorption of Nb4polarons, is observed, even at room temperature and above, in pure SBN, SBN :Cr or SBN:Ce crystals after previous reduction treatment at T>800 degrees C in Ar, vacuum or H-2. The absorption spectrum of Nb4+ polarons in reduced SBN crystals shows a considerable dichroism, which exists even far above r oom temperature. The spectral shape of the Nb(4+)polaron absorption shifts to higher energies with decreasing temperature. The concentration of polaro ns can be estimated from the magnetic susceptibility[1] and yields a value of the optical oscillator strength f approximate to 5 x 10(-2) for the NIR- absorption.