E. V. Antipov

High-pressure effects in fluorinated HgBa2Ca2Cu3O8 + δ

We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O8 + δ (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high Tc record (166 K±1 K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic a-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the a-axis is one of the keys that controls the Tc of high-temperature superconductors.

Neutron scattering for analysis of processes in lithium-ion batteries

The review is concerned with analysis and generalization of information on application of neutron scattering for elucidation of the structure of materials for rechargeable energy sources (mainly lithium-ion batteries) and on structural rearrangements in these materials occurring in the course of electrochemical processes. Applications of the main methods including neutron diffraction, small-angle neutron scattering, inelastic neutron scattering, neutron reflectometry and neutron introscopy are considered. Information on advanced neutron sources is presented and a number of typical experiments are outlined. The results of some studies of lithium-containing materials for lithium-ion batteries, carried out at IBR-2 pulsed reactor, are discussed. The bibliography includes 50 references.

Synthesis and properties of NbM2RCu2O8 and TaM2RCu2O8 phases (MBA, Sr: RPr, Nd, Sm, Eu and Gd)

Abstract NbM 2 RCu 2 O 8 and TaM 2 RCu 2 O 8 (M Ba, Sr; R Pr, Nd, Sm, Eu and Gd) phases were synthesized. Electron diffraction study of TaSr 2 EuCu 2 O 8 showed the presence of a weak superstructure ( a = 82a 07 ), like that found for a number of similar phases. Rietveld refinement of this structure based on X-ray powder diffraction data was carried out in the space group P 4/ mmm ( R 1 = 0.038, R p = 0.037) since no superstructure reflections were observed. Various types of cation replacement were performed in order to increase the copper valence. Monophasic Nb(Ta) 1 , Ti,Sr 2 EuCu 2 O 8 samples were synthesized at P ( O 2 ) = 1 bar and T = 1050°C up to x = 0.1 (Nb) and 0.3 (Ta), but no superconductivity was detected down to 12 K. High pressure syntheses were carried out to obtain Nb(Ta)Sr 2 Eu 1 , Ca, Cu 2 O 8 phases, but they were found to have a narrow homogeneity range that provides no opportunity of inducing superconductivity in such a way.

Mercury nonstoichiometry of the Hg1−xBa2CuO4+δ superconductor and the P(Hg)–P(O2)–T phase diagram of the Hg–Ba–Cu–O system

Abstract The P (Hg)– P (O 2 )– T phase diagram of the Hg–Ba–Cu–O system for the Ba:Cu=2:1 ratio was experimentally studied and followed by means of the thermodynamic modeling. It was shown that the Hg 1− x Ba 2 CuO 4+ δ (Hg-1201) superconductor possesses a significant range of Hg-nonstoichiometry and exists in a certain P (Hg), P (O 2 ) and T range. Mercury nonstoichiometry of Hg-1201 was investigated in the 923⩽ T ⩽1095 K; 2.0⩽ P (Hg)⩽8.4 atm; 0.09⩽ P (O 2 )⩽0.86 atm ranges. It was found that the mercury content varies in the range of 0.80–0.94 under these conditions. The Gibbs energy of the Hg-1201 phase was estimated as a function of temperature and mercury concentration. The obtained results allow optimizing the synthesis conditions of Hg-1201 with a given Hg-content including preparation of the Hg-stoichiometric phase.

Thermodynamic properties of HgBa2CuO4+δ

Abstract Thermodynamic properties of the HgBa 2 CuO 4+ δ superconductor with different extra oxygen ( δ ) content and Ba 2 CuO 3.05 were investigated by a method of solution calorimetry. The formation enthalpy values of HgBa 2 CuO 4+ δ from oxides (HgO, BaO and CuO) for different δ were obtained (−102.0±3.3 kJ/mole for δ =0.02; −113.3±3.2 kJ/mole for δ =0.08; −116.8±3.1 kJ/mole for δ =0.11). The obtained data show that the HgBa 2 CuO 4+ δ superconductor is thermodynamically stable at room temperature with regard to decomposition into Ba 2 CuO 3.05 and mercury oxide. Moreover, its oxidation by oxygen decreases significantly the formation enthalpy, and, therefore, should take place in the studied range of δ variation.

Formation of magnetic moments in the cuprate superconductor Hg0.8Cu0.2Ba2Ca2Cu3O8+δ below Tc seen by NQR

We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer highTc-compounds HgBaCaCuO and HgBaCaCuO(F) with Tc ¼ 134 K. Above Tc two Cu NQRline pairs are observed in the spectra corresponding to the two inequivalent Cu lattice sites. Below Tc the Cu NQRspectra show additional lines leading to the extreme broadened Cu NQRspectra at 4.2 K well known for the HgBaCaCuO compounds. The spin– lattice relaxation curves follow a triple exponential function with coefficients depend onto the saturation time (number of saturation pulses), whereas the spin–spin relaxation curve is described by a single exponential function. From the spin–lattice relaxation we deduced a complete removal of the Kramers degeneracy of the Cu quadrupole levels indicating that the additional lines are due to a Zeemann splitting of the 63=65 Cu lines due to the spontaneous formation of magnetic moments within the CuO layers. Below 140 K, the spectra are well fitted by a number of 6 63=65 Cu line pairs. From the number of the Cu lines, the position of the lines relative to each other and the complete removal of the Kramers degeneracy we deduced an orientation of the magnetic moments parallel to the c-axis with magnitudes of the order of 1000 G. We also discuss the possible microscopic origin of the observed internal magnetic fields. 2004 Elsevier B.V. All rights reserved.

Synthesis and characterization of HgBa2RCu2O6+δ (R = Eu, Gd, Ho, Er, Tm, Yb and Y)

Abstract Compounds with the general formula HgBa 2 RCu 2 O 6+δ (Hg-1212 phase, R = Eu, Gd, Ho, Er, Tm, Yb and Y) were synthesized by solid state reaction. The influence of synthesis conditions on the phase composition of these samples was investigated. X-ray powder and electron diffraction data have shown that all synthesized compounds are isostructural with the Hg-1212 phases containing rare earth elements of larger ionic radius, already published in literature. Different thermal annealings performed on the samples showed the impossibility of substantially changing the oxygen content of the synthesized compounds. Measurements of the temperature dependence of the magnetic susceptibility showed no diamagnetic signal down to 12 K.

Crystal structure of the pyrovanadate K4V2O7

The crystal structure of anhydrous K4V2O7 (I) is determined by powder X-ray diffraction. The compound crystallizes in the monoclinic system (a = 10.222(1) Å, b = 6.2309(8) Å, c = 7.282(1) Å, β = 101.31(1)°, space group C2/m, Z = 2). The structure contains layers of isolated V2O7 pyrovanadate groups separated by layers of potassium cations. The hydration and dehydration of I are studied by thermal analysis and high-temperature X-ray diffraction. The dehydration is accompanied by decomposition of the starting crystal hydrate to give intermediate compounds. Anhydrous compound I undergoes a reversible phase transition at 740°C. The high-temperature phase is assumed to have a hexagonal unit cell (a = 6.169(4) Å, c = 15.72(1) Å, Z = 2).

Zeeman splitting of the 63,65Cu NQR line in optimally doped Hg1Ba2Ca2Cu3O8+δ below Tc

Abstract We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer compound Hg 1 Ba 2 Ca 2 Cu 3 O 8+ δ (Hg-1223) with T c =134 K. Above T c two Cu line pairs are observed in the spectrum corresponding to the two inequivalent Cu lattice sites. Below T c the Cu NQR spectrum shows a splitting of these two line pairs into six line pairs. From a multiexponential spin lattice relaxation with a dependency on the initial conditions, we find a formation of magnetic moments in the CuO layers as the origin of the line splitting. Furthermore, the magnetic moments are oriented parallel to the symmetry axis of the electrical field gradient tensor with magnitudes of the order of 1000 G.

Transition-Metal Perovskites

Perovskites are one of the most important classes of inorganic materials, thanks to a variety of their functional properties and inherent chemical and structural flexibilities. This chapter provides a brief review on crystal chemistry and crystallography of perovskites with emphasis on the achievements made within the last 10–15 years. The topics covered include cooperative octahedral tilting distortions in perovskites, lone-pair-driven and electronic instabilities, ordering phenomena at cation and anion sublattices, and aperiodic order in perovskites and mixed-anion perovskites.