S. Kh. Estemirova

Phase transitions in manganites with substitution of divalent ions for manganese

Experimental data are presented for the position of phase boundaries “orthorhombic-rhombohedral structure” and “semiconductor-metal” in manganites of La1 − c + xSrc − x2+Mn1 − xMex2+O3 + γ (Me = Mg, Zn, Ni) systems depending on the concentration of substituting divalent cations (0.15 ≤ c ≤ 0.35; 0.025 ≤ x ≤ 0.100).

Homogeneity range of neodymium manganite in air

The solubility boundaries for Nd2O3 and manganese oxides in NdMnO3 ± δ have been determined by X-ray powder diffraction analysis of homogeneous phases and heterogeneous compositions of the general formula Nd2 − xMnxO3 ± δ (0.90 ≤ x ≤ 1.20; Δx = 0.02) prepared by ceramic technology from constituent oxides in air in the temperature range 900–1400°C. The results are presented in the form of a fragment of the Nd-Mn-O phase diagram in air. It is suggested that the Nd2O3 solubility in NdMnO3 ± δ is due to crystal defects and the solubility of manganese oxides is in addition due to the disproportionation reaction 2Mn3+ = Mn2+ + Mn4+ and the subsequent partial substitution of divalent for tervalent manganese ions in the cuboctahedral positions of the perovskite-like crystal lattice. To verify this suggestion, it is necessary to systematically study the oxygen nonstoichiometry δ in Nd2 − xMnxO3 ± δ as a function of x and synthesis temperature and structurally study this oxide with these parameters being varied.

State of oxygen in the structure of YBa2Cu3O6+δ: Reversible changes during annealing and their influence on Tc

The valence state of oxygen in YBa2Cu3O6+δ has been studied by x-ray photoelectron spectroscopy. The results indicate that, in the temperature range 298–510 K, the state of some of the cations in this compound changes significantly. These changes are interpreted in terms of ordered and disordered states in the anion sublattice of YBa2Cu3O6+δ, the boundary between which lies within the temperature range studied. Oxygen ordering is assumed to play a central role in determining the complex, stepwise variation of the superconducting transition temperature with composition.

Phase composition and structure of La1 − x Cax MnO3 + δ (0 ≤ x ≤ 0.2) solid solutions

A structural phase diagram of La1 − xCaxMnO3 + δ (0 ≤ x ≤ 0.2) solid solution in air has been constructed for the first time, and the equilibrium T-x fields of the monoclinic, orthorhombic, and rhombohedral phases in this system have been outlined. The transitions between these phases are accompanied by sharp changes in lattice parameters, suggesting that they are first-order.

Magnetic and structural inhomogeneities of the La1 − x Ca x MnO3 + δ manganites

The specific features revealed in the behavior of the parameters of the crystal structure and the lattice dynamics of the La1 − xCaxMnO3 + δ manganites upon the transition to a magnetically ordered state are investigated using X-ray powder diffraction and inelastic neutron scattering. The results obtained are explained in terms of an inhomogeneous state of the samples. This state manifests itself in the form of local regions that are enriched or depleted in charge carriers, with the former regions characterized by the highest temperature of ferromagnetic ordering in the system under investigation. A comparison of the evolution of the crystal structure with variations in the temperature both in the presence and in the absence of a magnetic field has demonstrated that the inhomogeneities are eliminated by an external magnetic field and that the regions enriched in charge carriers become predominant in the system.

Effect of Titanium Additions on the Thermophysical Properties of Glass-Forming Cu 50 Zr 50 Alloy

Differential scanning calorimetry, laser flash method, and dilatometry were used to study the thermophysical properties of quenched Cu50Zr50–xTix (x = 0, 2, 4, 6, 8) alloys in the temperature range from room temperature to 1100 K. Data obtained on the heat capacity, thermal diffusivity, and density have been used to calculate the coefficient of thermal conductivity. Temperatures corresponding to the stability of martensite CuZr phase, its eutectoid decomposition, and formation in Cu50Zr50–xTix alloys with different Ti contents upon heating have been determined. It has been found that the thermal diffusivity and thermal conductivity of the studied alloys are low and a typical of metallic systems. As the titanium content increases, the coefficients of thermal conductivity and thermal diffusivity vary slightly. It has been shown that the low values of thermophysical characteristics correspond to the better capability of amorphization and can be a criterion for the glass-forming ability of Cu–Zr-based alloys.

Peculiarities of the martensitic transformation in (Cu0.5Zr0.5)100−xAlx glass-forming alloys

ABSTRACT We systematically study peculiarities of the martensitic transformation (MT) in glass-forming alloys focusing on the one. We obtain that an addition of aluminum to the binary alloy leads to a decrease of both the martensite and the austenite start temperatures. The former reaches the room temperature area for the alloy. The martensitic transition proceeds as two-stage transformation of the CuZr B2 phase in two monoclinic phases (P21/m and Cm). The proceeding of the MT depends on annealing temperature. It is also shown that fast quenching of the samples in liquid nitrogen leads to the same MT as observed at slow cooling.

Relationship Between Electronic and Crystal Structure in Nd 1 + x Ba 2 − x Cu 3 O 6 + δ

In accordance with a relation between the lattice parameter c and the concentration of holes p, which has been found earlier for the YBa2Cu3O6+δ compound, we obtain the p parameter in the same manner for the solid solution Nd1.2Ba1.8Cu3O6+δ with substitution of Nd3+ for Ba2+ in barium sites. For this, structural and superconducting properties of the Nd1.2Ba1.8Cu3O6+δ samples stored for specified times τ after quenching from annealing temperatures have been studied. The investigation shows that Nd1.2Ba1.8Cu3O6+δ stored for a long time has quite a low critical temperature Tc extending only to Tconset

Properties of La–Sr Manganites with Combined Substitution of Different Valence Ions for Strontium and Manganese

T_{\mathrm {c}}^{\text {onset}}

Crystallization kinetics of rapidly quenched Cu50Zr50 and Cu46Zr46Al8 glass-forming alloys

= 55 K for the most oxidized sample with δ = 0.953. We find that the δ-dependence of the lattice parameter c significantly changes with time τ. When using the relation between c and p, the existence of electron doping of 0.045 per Cu in Nd1.2Ba1.8Cu3O6+δ can be inferred. This doping explains well-reduced Tc in Nd1.2Ba1.8Cu3O6+δ. In addition, we observe a local drop of Tc by up to 20 K for the samples with p˜0.095 (δ˜0.8) similar to decreasing Tc known as “anomaly 1/8”.