Effect of ethylene glycol on the formation of extended crystals of M1/3Co2/3C2O4 · 2H2O (M = Zn, Mn) oxalates and their thermolysis products

The effect of ethylene glycol (EG) on the formation of whiskers and fibers of complex oxides with the general formula MCo₂O₄ upon the thermolysis of M_1/3Co_2/3C₂O₄ (M = Zn, Mn) oxalates has been studied. New compounds (solvates) are formed when powdered oxalates are heated with EG. In the solvates, EG molecules substitute for water molecules according to the reaction M_1/3Co_2/3C₂O₄ · 2H₂O + HOCH₂CH₂OH = M_1/3Co_2/3C₂O₄(HOCH₂CH₂OH) + 2H₂O. The solvates have been characterized using X-ray powder diffraction, microscopy, IR spectroscopy, thermogravimetry, and chemical analysis. The shape, structure, and particle size of the thermolysis products of EG-modified oxalates have been determined using scanning electron microscopy.     

<Superscript>63</Superscript>Cu and <Superscript>139</Superscript>La NMR and chemical bonding in anion-deficient perovskite LACu<Subscript>0.81</Subscript>Ni<Subscript>0.19</Subscript>O<Subscript>2.5+δ</Subscript>

The ⁶³Cu and ¹³⁹La NMR spectra of the low-(δ = 0.25) and high-temperature (δ = 0) phases of lanthanum cuprate LACu_0.81Ni_0.19O_2.5+δ have been obtained. Quantum chemical calculations of the electronic structure of the high-temperature phase have been performed. It is found that the observed metal-semiconductor phase transition is attended by changes in the degree of atomic ordering and in the character of electronic conductivity over certain types of “copper” centers.     

Synthesis and magnetic properties of the complex oxide La<Subscript>1.5</Subscript>Sr<Subscript>1.5</Subscript>CuMnO<Subscript>6.67</Subscript>

A new oxide phase, La_1.5Sr_1.5CuMnO_6.67, related to the Ruddlesden-Popper homologous series A _{n + 1}B _n O_{3n + 1} (n = 2) was synthesized. The magnetic susceptibility of the obtained compound obeys the Curie-Weiss law above 114 K. At 14 K, a magnetic anomaly related to the transition to the spin-glass state was detected.     

Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

The reactions of ethylene glycol with manganese oxalates MnC₂O₄ · 2 H₂O and MnC₂O₄ · 3H₂O on heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from oxalates to give a new solvate compound according to the reaction MnC₂O₄ · nH₂O + HOCH₂CH₂OH = MnC₂O₄(HOCH₂CH₂OH) + nH₂O↑. The crystals of the solvates retain the morphology of the initial oxalates, which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC₂O₄ · 3H₂O and MnC₂O₄(HOCH₂CH₂OH) having quasi-unidimensional structure gave Mn₃O₄ and Mn₂O₃ nanowhiskers in air and MnO in an inert gas environment. Heating of MnC₂O₄ · nH₂O in ethylene glycol at temperatures above 100°C results in anhydrous manganese oxalate.     

Magnetic phases in lanthanum-strontium manganite-cobaltite La1.25Sr0.75MnCoO6

Two methods—the solid-phase high-temperature (1300 °C) and the liquid-phase low-temperature (750 °C) routes—were used to synthesize the complex oxide La_1.25Sr_0.75MnCoO₆, which has the structure of rhombohedral perovskite and is characterized by a disordered distribution of Mn and Co in structural sites. It was found by means of X-ray absorption near edge spectroscopy (XANES) at the K-edge that mixed valence states of Co²⁺/Co³⁺ and Mn³⁺/Mn⁴⁺, exist in both phases. Measurements of dc magnetization and real (χ′) and imaginary (χ″) parts of the ac susceptibility showed that the magnetic properties of these oxides are determined by a ferromagnetic transition at T_C=217 K and a frequency-dependent transition at T_g<100 K. The high frequency dependence of T_g is indicative of the cluster-glass behavior of La_1.25Sr_0.75MnCoO₆ (7 5 0) at T<T_C within the ferromagnetic state.     

Synthesis and magnetic properties of a new layered oxide La<Subscript>1.5</Subscript>Sr<Subscript>1.5</Subscript>Mn<Subscript>1.25</Subscript>Ni<Subscript>0.75</Subscript>O<Subscript>6.67</Subscript>

A new oxide phase La_1.5Sr_1.5 Mn_1.25Ni_0.75O_{6.67 ± 0.05}, a member of the A_{n + 1} BnO_3n+1(n=2) Rad-dlesden—Popper homologue series, was synthesized, and its structure and magnetic properties characterized. Magnetic anomalies associated with the competition between antiferromagnetic and ferromagnetic orders are observed in the range of the temperatures studied (2-400 K). The ESR spectra of the compound feature the constriction of a magnetic signal and a shift toward g(Mn⁴⁺).     

Phase equilibria in the system CaO-CoO-Co<Subscript>2</Subscript>O<Subscript>3</Subscript>-MnO-MnO<Subscript>2</Subscript>

Phase equilibria in the system CaO-CoO-Co₂O₃-MnO-MnO₂ at 700–1200°C in air were studied on the basis of published data and proper experiments. No new compounds were found. The results are presented in the form of 13 isothermal sections of the phase diagram.     

Phase Equilibria in the System CuO-Fe2O3-Sb2O4-O2

Results of X-ray phase analysis were used to construct the phase diagram of the system CuO-Fe₂O₃-Sb₂O₄-O₂ at 1000°C in air. Two Cu_2x Fe_4-3x Sb _x O₆ solid solutions (0 x 0.154 and 0.923 x 1) of, respectively, hematite and bixbyite structure were identified.     

EPR study of quasi-one-dimensional complex oxides A3n + 3mA′nMn3m + nO9m + 6n (A-Sr, Ba; A′-Mg, Zn, Cu)

Exchange interactions in the quasi-one-dimensional complex oxides Sr₄MgMn₂O₉, Ba₆MgMn₄O₁₅, Ba₈MgMn₆O₂₁, and Ba₉ M ₂Mn₅O₂₁ (M-Cu, Zn, Mg) have been studied by electron paramagnetic resonance. The temperature dependence of the spectral parameters showed that the exchange interaction is antiferromagnetic and occurs mainly inside the manganese-containing groups and to a lesser extent between them.