Hydrothermal synthesis and transport property of cubic KNb0.77Al0.23O2.77

Cubic KNb0.77Al0.23O2.77 is initially synthesized by low temperature hydrot hermal synthesis, whereas high temperature ceramic method can only produce the orthorhombic phase of the parent KNbO3 structure. By tuning the niobium species and KOH concentration, we have obtained orthorhombic KNbO3 and an intermediate phase. The cubic product was examined by X-ray diffraction, di fferential scanning calorimeter, and X-ray photoelectron spectroscopy. High temperature treatment up to 1 000 degrees C did not result in phase transi tion, reflecting a high structural stability, The transport mechanism,can b e ascribed to the small polarons. However for the orthorhombic counterpart, the discontinuty may be arised from the structural transformation due to t he structural instability.