X-ray absorption spectra and ferroelectricity in pyrochlore niobates

Nara, Shintaro*; Torigoe, Shuhei*; Hanasaki, Noriaki*; Nogami, Yoshio*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo

no journal, , 

We have investigated the physical properties of pyrochlore niobates YCaNbO and NdCaNbO. From synchrotron X-ray absorption and thermogravimetric measurements, the average valence of Nb ion in these oxides was determined as 4.5+, indicating the existence of charge frustration on the Nb site. These oxides have been found to show some intriguing properties such as the absence of magnetic moment of Nb, large thermoelectric effect and ferroelectricity. Possible origins of these phenomena are discussed on the basis of results of X-ray absorption measurements.