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Abstract
Potassium Niobate (KNbO3) doped with Iron is a well known photorefractive material in theoptical region. There is, however, a need for photorefractive materials in the near infrared
(NIR). Chromium doped KNbO3 has been suggested as a possible candidate, and computer
calculations and modeling show a photorefractive response above 0.4 eV in earlier studies.
The latest studies have the photorefractive effect at 1 eV. Due to the volatility of K2O
it is problematic to fabricate KNbO3:Cr3+ as a congruent crystal. In this work, single
phase (Cr3+) doped KNbO3 was fabricated using the sol-gel method, which allows us to
make a polycrystalline ceramic at low temperatures. Metal alkoxides, potassium ethoxide
and niobium pentaethoxide were used as the precursor material. KNbO3:x% Cr3+ were
successfully prepared by reflux at 120 ◦C. The Cr3+ concentration in the host varied between
0.005 and 0.1 mol%. The obtained polycrystalline powder was characterized by using X-ray
diffraction (XRD). No secondary phases were found in any of the doped or undoped samples,
suggesting single phase orthorhombic KNbO3. The X-ray diffraction data was used to study
the effects of peak broadening by using the Williamson-Hall analysis technique. This was
done in order to find the microstrain and crystallite size; to better understand changes in
intensity of X-ray diraction peaks as the concentration of trivalent chromium increased.
Applying the madelung potential energy using the VESTA computer program and nearest
neighbor potential energies the possible energy level that the Cr3+ ion lies within the host
KNbO3 was found. Further it appears that these theoretical calculations find agreement
with prior theoretical models that established the ionization threshold of the chromium ions.