NIR absorption of Nb4+ polarons in reduced SBN crystals

A stable broad absorption band around 0.72 eV, assigned to the absorption o f Nb4+ polarons, is observed in pure SBN, SBN:Cr or SBN:Ce crystals after p revious 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 consid erable dichroism, which exists even far above room temperature. The peak po sition and the integrated absorption of Nb4+ polarons are measured as a fun ction of temperature. The maximum of the Nb4+ polaron absorption shifts to higher energies with decreasing temperature. A comparison of optical absorp tion and recent literature values [1] of the magnetic susceptibility and th erefore concentration of polarons yields values of the optical oscillator s trength estimated to be f approximate to (5 +/- 0.6) x 10(-2).