The average valence, ValO, of the oxygen anions in the perovskite oxide BaTiO3, was found using O1s photoelectron spectra to be −1.55. This experimental result is close to the theoretical value for BaTiO3 (−1.63) calculated by Cohen [Nature 358, 136 (1992)] using density functional theory. Using the same approach, we obtained values of ValO for several monoxides, and investigated the dependence of ValO and the ionicity on the second ionization energy, V(M2+), of the metal cation. We found that the dependence of the ionicity on V(M2+) in this work is close to that reported by Phillips [Rev. Mod. Phys. 42, 317 (1970)]. We therefore suggest that O1s photoelectron spectrum measurements should be accepted as a general experimental method for estimating the ionicity and average valence of oxygen anions.

Powder samples of the ferrites MxNi1−xFe2O4 (M = Cr, Co and 0.0 ≤ x ≤ 0.3) were prepared using a chemical co-precipitation method. X-ray diffraction analysis showed that the two series of samples had a single-phase cubic spinel structure. It was found that the magnetic moments (μexp) per formula of samples measured at 10 K decreased when Cr substituted for Ni, but increased when Co substituted for Ni, in spite of the fact that the magnetic moments of Cr2+ (4 μB) and Co2+ (3 μB) are higher than that of Ni2+ (2 μB). With the assumption that the magnetic moments of Cr2+ and Cr3+ lie antiparallel to those of the Fe, Co, and Ni cations in the same sublattices of spinel ferrites, the dependences on the Cr (Co) doping level of the sample magnetic moments at 10 K were fitted successfully, using the quantum-mechanical potential barrier model earlier proposed by our group. For the two series of samples, the fitted magnetic moments are close to the experimental results.

We report the crystal growth of a new compound, Yb 3 Os 4 Ge 13 , by using a Bi-flux method.X-ray diffraction measurement shows that it crystallizes in the quasi-skutterudite-type caged structure with a cubic space group of . Magnetic measurements reveal almost fully localized Yb f-moments above 120 K. The resistivity exhibits a crossover from metallic to insulating behavior with a logarithmic increase below ~ 40 K. The specific heat coefficient shows a rapid upturn below ~5 K and exceeds 2 J mol -1 K -2 at 2 K. Our experimental analysis and electronic band structure calculations demonstrate that Yb 3 Os 4 Ge 13 exhibits the Kondo effect due to strong hybridization of the localized Yb f-moments with the p-electrons of the surrounding Ge-cages.

Ti-doped Ni 0.68 Fe 2.32 O 4 spinel ferrite samples with nominal composition Ni 0.68À0.8x Ti x Fe 2.32À0.2x O 4 (0 x 0.312) were prepared using conventional ceramic methods. The samples exhibited a single-phase cubic spinel structure. When the doping level had values x > 0.15, a transition temperature, T N , was found, below which the magnetization of the samples decreased with decreasing measurement temperature. This phenomenon indicates that an additional antiferromagnetic structure arises in the traditional spinel phase of ferrites resulted from Ti doping. Therefore, Ti ions appear in the form of Ti 3þ and Ti 2þ cations that have magnetic moments, rather than as Ti 4þ cations without magnetic moment as assumed by many researchers. The dependence of the magnetic moments on the Ti doping level x at 10 K was fitted successfully using our quantum-mechanical potential barrier model proposed earlier. In the fitting process, we assumed that the magnetic moments of the Ti cations were opposite to the direction of the Fe and Ni moments. According to the fitted results, the Ti 2þ cations at the [B] sites constitute about 81% of the total Ti content x for all samples, which is close to the content of the Ni 2þ cations at the [B] sites (77%).

Ferrite powder samples of Mn x Ni 1-x Fe 2 O 4 (0.0 x 1.0) with single phase (A)[B] 2 O 4 spinel structure were prepared using a sol-gel method. Following the successful proposal by our group, that the magnetic moment directions of Cr 2þ (3d 4 ) cations are antiparallel to those of Fe 3þ (3d 5 ) and Fe 2þ (3d 6 ) cations in a given sublattice of the Cr-doped spinel ferrites due to the constraints imposed by Hund's rules, we extend here the same idea and assume that the magnetic moment directions of Mn 3þ (3d 4 ) cations are also antiparallel to those of Mn 2þ (3d 5 ) and divalent and trivalent Fe (Ni) cations in a given sublattice of Mn-doped spinel ferrites. We have thereby obtained cation distributions for the samples by fitting the magnetic moments of the samples at 10 K. The results indicate that 72% of the Mn cations occupy the [B] sites in MnFe 2 O 4 , which is close to the results for Ni (82%) in NiFe 2 O 4 , but is different from the result obtained using the conventional view which yields 80% of the Mn cations in the (A) sites of MnFe 2 O 4 . On the basis of the present analyses of the magnetic structure of Mn x Ni 1-x Fe 2 O 4 (0.0 x 1.0), we propose here a new model for spinel ferrites that is distinctly different from both the super-and the doubleexchange model and that we refer to as the O2p itinerant electron model. Using this model, not only can the magnetic structure of the spinel ferrites MFe 2 O 4 (M ¼ Fe, Co, Ni, and Cu) be explained better than by using the super-and doubleexchange interaction models, but also the magnetic structure and the cation distributions of Cr-, Mn-, and Ti-doped spinel ferrites can be explained.