XPS spectroscopy, structural, magnetic and dielectric investigations of CaGdAlO4 and Yb:CaGdAlO4 single crystals

Materials for ultrafast femtosecond lasers, CaGdAlO4 (CGA) single crystals, undoped and doped nominally with 8% at. of Yb, were grown by the Czochralski method in [100] direction. X-ray analyses showed the ideal disorder on Gd/Ca sites. The decrease of unit cell volume for the crystal doped with Yb was observed. Magnetic measurements revealed that undoped and doped samples were paramagnetic. The real concentration of Yb was determined as 5% at. The XPS lines: O1s, Al2p and Ca2p are complex and they consist of the main line and additional lines at lower and higher binding energy. The intensities of additional lines decrease comparing the end and cone part of crystal, indicating an improvement of crystal structure during the growth process. XPS chemical analyses showed deficiency of Al and Ca and excess of oxygen. The oxygen excess may exist in two contributions: in one, to keep the charge neutrality as Gd-Ox sheets between CGA; the second as interstitial oxygen, responsible for brownish coloration of crystals. Dielectric properties are close to values measured for similar compounds CaYAlO4, CaNdAlO4, and SrLaAlO4.