I. A. Zvereva

Phase diagram of the LaFeO3-LaSrFeO4 system

The phase relationships in the LaFeO3-LaSrFeO4 system at temperatures in the range 1000–2100°C in air are investigated, and the phase diagram of the system is constructed. One perovskite-like compound, namely, La2SrFe2O7, which belongs to the Ruddlesden-Popper phases, is revealed in the system.

Photocatalytic properties and hydration of perovskite-type layered titanates A2Ln2Ti3O10 (A = Li, Na, K; Ln = La, Nd)

Layered perovskite-type oxides A2Ln2Ti3O10 (A = Li, Na, K; Ln = La, Nd) prepared by solid-phase synthesis and their hydrated forms were characterized by the methods of TGA, XRD, and by UV-Vis spectroscopy. Photocatalytic activity of A2Ln2Ti3O10 oxides in reaction of hydrogen evolution from aqueous alcoholic suspensions irradiated by UV-light was studied. It was shown that the ability to intercalation of water into interlayer space essentially affects the rate of photoinduced hydrogen evolution and is a determining factor leading to a high photocatalytic activity.

Mechanism of formation of the complex oxide Gd2SrFe2O7

The mechanism of formation of the perovskite-like layered structure of the oxide Gd2SrFe2O7 was studied. The limiting stages are those of formation of phases with perovskite (GdFeO3, SrFeO3−x) and K2NiF4 (GdSrFeO4) structures. The Mössbauer study has shown that iron atoms exist in a heterovalent state (Fe3+ and Fe4+) only in the structure of SrFeO3−x).

Ion-Exchange Reactions in the Structure of Perovskite-like Layered Oxides: I. Protonation of NaNdTiO 4 Complex Oxide

The behavior of perovskite-like NaNdTiO4 complex oxide in acid aqueous solutions was studied. By the X-ray and thermogravimetry analyses the instability of NaNdTiO4 in aqueous solutions was found, which is determined by the sodium cation exchange for protons and by water molecules intercalation into the interlayer space of the crystal structure. The proton-containing layered oxides HNdTiO4 and HxNa1−xNdTiO4·yH2O were obtained (1 < x < 0.64, 0 < y < 0.47). The structure of the H0.73Na0.27NdTiO4·0.3H2O compound was refined.

Formation of the complex oxide NaNdTiO4

The processes of phase formation in the Na2CO3-TiO2 and Na2CO3-TiO2-Nd2O3 systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO4 compound occurs through the reaction of the intermediate product Na8Ti5O14 with neodymium oxide in the temperature range 720–780°C. The optimum method is proposed for synthesizing NaNdTiO4, which makes it possible to reduce the temperature of the synthesis, to avoid the formation of impurities, and to obtain the product in a finely dispersed state.

Phase formation during synthesis of the LaSr2Mn2O7 compound

The processes of formation of the LaSr2Mn2O7 compound are investigated in the temperature range 800–1400°C. The formation of the LaSr2Mn2O7 compound is found to occur through intermediate phases, namely, LaMnO3 and Sr2MnO4. It is revealed that the decomposition of the LaSr2Mn2O7 compound is caused by a decrease in both the temperature and the oxygen pressure.

Polar Nature of (CH3NH3)3Bi2I9 Perovskite-Like Hybrids

High-quality single crystals of perovskite-like (CH3NH3)3Bi2I9 hybrids have been synthesized, using a layered-solution crystal-growth technique. The large dielectric constant is strongly affected by the polar ordering of its constituents. Progressive dipolar ordering of the methylammonium cation upon cooling below 300 K gradually converts the hexagonal structure (space group P63/mmc) into a monoclinic phase (C2/c) at 160 K. A well-pronounced, ferrielectric phase transition at 143 K is governed by in-plane ordering of the bismuth lone pair that breaks inversion symmetry and results in a polar phase (space group P21). The dielectric constant is markedly higher in the C2/c phase above this transition. Here, the bismuth lone pair is disordered in-plane, allowing the polarizability to be substantially enhanced. Density functional theory calculations estimate a large ferroelectric polarization of 7.94 μC/cm2 along the polar axis in the P21 phase. The calculated polarization has almost equal contributions of the methylammonium and Bi3+ lone pair, which are fairly decoupled.

Soft Chemistry Synthesis of Complex Oxides Using Protonic Form of Titanates HLnTiO4 (Ln=La, Nd)

In the present work protonic forms of layered n=1 Ruddlesden-Popper oxides HLnTiO4 (Ln=La, Nd) were used as starting point for synthesis of three series of the perovskite-like compounds. Characterization by SEM, powder XRD and TGA has been performed for the determination of the structure and composition of synthesized oxides.

Study of photocatalytic activity of layered oxides: NaNdTiO4, LiNdTiP4, and HNdTiO4 titanates

The catalytic activity of the perovskite-like layered oxides NaNdTiO4, LiNdTiO4, and HNdTiO4 in the reaction of the methyl orange dye decomposition under the action of UV irradiation was studied. Rate constants of the pseudo-first order were determined. It was found that in the series NaNdTiO4, HNdTiO4, and LiNdTiO4 the photocatalytic activity of the layered oxides increases.

Mechanism and kinetics of formation of La2SrFe2O7 and Nb2SrFe2O7

Phase formation processes in the systems Ln2O3-SrO-Fe2O3 (Ln = La, Nd) in air in the temperature range 1200–1500°C were studied. The synthesis of the complex ferrites La2SrFe2O7 and Nb2SrFe2O7 involves the formation of the intermediate compounds LnFeO3 and LnSrFeO4 and occurs by the same mechanism as the synthesis of the corresponding aluminates, but much faster.