Кристаллохимия и магнитные свойства гексаферрита BaFe-=SUB=-12-=/SUB=-O-=SUB=-19-=/SUB=- при гетеровалентном замещении железа цирконием

Samples of BaFe12O19 M-type barium hexaferrite with partial iron substitution by zirconium ions (concentration up to 10 at.%) have been synthesized and investigated. Studies of crystal features, phase composition, and magnetic properties were carried out using X-ray diffraction, Mössbauer spectroscopy, and VSM respectively. The presence of limited heterovalent isomorphism by the 2Fe3+ → Zr4+ + Fe2+ mechanism was shown. The limit of heterovalent isomorphic substitution by zirconium ions in barium hexaferrite (x = 0.6) was established. It was noted that additional sextets in the Mössbauer spectra of barium hexaferrite can be formed during the localization of Zr4+ ions predominantly in the 12k and 4f2 positions due to the frustration of the magnetic structure. The correlation between the chemical composition (concentration of zirconium ions), impurity phase formation, the peculiarities of the distribution of substituents over oxygen coordination, and the magnetic properties was established.

Особенности катионного распределения и магнитных свойств поликристаллических гексагональных ферритов BaFe-=SUB=-12-x-=/SUB=-Sn-=SUB=-x-=/SUB=-O-=SUB=-19-=/SUB=-

The cation distribution and magnetic properties of polycrystalline ВаFe12–xSnxO19 (х = 0.0, 0.1, 0.3, 0.6, 0.9 and 1.2) ferrites have been studied for the first time by Fe57 and Sn119 Mössbauer spectroscopy. It was shown that doping of BaFe12O19 with tin is performed with limited heterovalent isomorphism according to the scheme 2Fe3+Sn4+ + Fe2+. It was found that intense heterovalent isomorphic substitutions occur in the 12k site of the BaFe12-xSnxO19 hexaferrite in the range of 0.1 < x < 0.6; less significant substitutions observed in the 4f2 and 2a sites. It was established that the heterovalent isomorphic substitution of tin for iron in BaFe12- xSnxO19 is limited by the values of x in range х = 0.6–0.9 Measurements of the magnetic parameters of the obtained samples were performed. The possibility of practical application of the synthesized ferrites is discussed.

Micro-Raman Spectroscopy Assessment of Chemical Compounds of Mantle Clinopyroxenes

The composition of clinopyroxenes is indicative for chemical and physical properties of mantle substrates. In this study, we present the results of Raman spectroscopy examination of clinopyroxene inclusions in natural diamonds (n = 51) and clinopyroxenes from mantle xenoliths of peridotites and eclogites from kimberlites (n = 28). The chemical composition of studied clinopyroxenes shows wide variations indicating their origin in different mantle lithologies. All clinopyroxenes have intense Raman modes corresponding to metal-oxygen translation (~300–500 cm−1), stretching vibrations of bridging O-Si-Obr (ν11~670 cm−1), and nonbridging atoms O-Si-Onbr (ν16~1000 cm−1). The peak position of the stretching vibration mode (ν11) for the studied clinopyroxenes varies in a wide range (23 cm−1) and generally correlates with their chemical composition and reflects the diopside-jadeite heterovalent isomorphism. These correlations may be used for rough estimation of these compounds using the non-destructive Raman spectroscopy technique.

Phase Diagram of LiF-Li3PO4 System: A New Mechanism of Heterovalent Anionic Isomorphism

ABSTRACTThe phase diagram of LiF-Li3PO4 system is studied. The eutectic coordinates are 800±5°C, 8±1 mol% Li3PO4. A region of a solid solution based on lithium phosphate with a length of up to 11±2 mol% LiF was discovered. It is assumed that there is heterovalent isomorphism where anionic tetrahedron (PO4)3- is replaced by tetrahedron (LiF4)3-.