Nano-scale chemical and structural segregation induced in surface layer of NaNbO3 crystals with thermal treatment at oxidising conditions studied by XPS, AFM, XRD, and electric properties tests

The process of ionic segregation in the surface layer induced by the thermal treatment of the NaNbO3 crystal was studied. The study of the as grown crystal and the crystal heated at 970 K in ambient air was carried out for comparison. The changes in the concentration of the elements within the surface layer were determined using XPS measurements. The AFM technique was applied to determine the surface morphology related to nano-scale transformation. The possibility of appearance of the Ruddlesden-Popper phases was detected by the XRD test. The change in the features of the electric permittivity, the loss tangent, and the electric conductivity was ascribed to the marked participation of the chemically modified surface layer in the measured effective electrical properties.