L. A. Klinkova

Thermal stability of Bi2O3

Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of an α-Bi2O3 sample revealed staged phase transitions in the range 720–800°C (at 720, 780, and 800°C) and the elimination of oxygen to the composition Bi2O2.967 during heating to 895°C in air at 16 K/min. In dynamic vacuum (p = 1.33 Pa) at 780–800°C, Bi2O3 consecutively transforms to a phase with the cubic γ-Bi2O3 structure and tetragonal Bi2O2.3−2.4. In the latter, electron diffraction in a transmission electron microscope (ED/TEM) shows a superstructure with the superstructure vector q110 ≈ 1/9, which indicates an ordered arrangement of oxygen vacancies.

Spatial Resolution of Transmission Electron Spectroscopy for the Study of Ordered Materials

The structure of barium-rich oxides of the Ba-Bi-O system was studied with the transmission electron spectroscopy (TEM) and electron diffraction techniques. The results show that TEM cannot reveal the presence of an ordered state in a material composed of irregular intergrown crystallites, if their sizes are less than several nanometers.

BaO-BiO1.5 phase diagram in the region 80-100 mol % BiO1.5 at po2 = 21 kPa

The phase equilibria in the region from 80 to 100 mol % BiO1.5 are studied in the BaO-BiO1.5 system in air and under an argon atmosphere using visual polythermal analysis (VPA), X-ray powder diffraction, differential thermal analysis (DTA), electron diffraction (ED), and elemental analysis in a transmission electron microscope (EA/TEM). A series of discrete layered rhombohedral phases (RPs) with the composition Ba2Bi8+nOy, where n = 0, 1, 2, 4, 8, or 10, is discovered. The melting character is determined for these RPs: the 1: 4 phase melts congruently; the 2: 9, 1: 5, 1: 6, and 1: 8 phases melt incongruently. The crystallization fields are 10–30°C. At po2 = 21 kPa, the 1: 4 phase in the subsolidus region decomposes into a 4: 13 perovskite-like phase and the 2: 9 phase. The other rhombohedral phases decompose into stages to yield Bi2O3 and a neighboring RP that is richer in barium. The Ba2Bi8+nOy oxides are stable in argon and experience a first-order phase transformation at about 560°C.

On the structure of melt in the BaO-CuOx (50.0–80.0 mol % CuO) system at p(O2) = 21 kPa

The composition of melt from the crystallization and liquidus regions of the BaO-CuOx phase diagram was studied within the range 50.0–80.0 mol % CuO at p(O2) = 21 kPa. At 900–1050°C, melt in the range of the compositions studied is structured and consists of oxides having cubic structure BaCuO2; (Ba/Cu = 0.80−0.96), tetragonal structure BaCu2O2; (Ba/Cu = 0.50−0.62), and monoclinic structure (CuO). The off-stoichiometry of BaCu2O2 manifests itself in electron diffraction (ED) patterns taken in a transmission electron micro-scope (TEM) as diffuse scattering streaks extending in the [100] and [010] directions. These data find explanation in the existence of clusters having a suggested composition of Ba2Cu3O3.5 + x which are produced by BaCu2O2 + x disproportionation and are integrated into the BaCu2O2 structure. Thermal effects observed in the liquidus region, which are accompanied with a change in oxygen content, are associated with the cluster structure of the melt and its evolution in response to varying temperature.

New phases in the barium-rich region of the BaO-BaCuO2 system

The phase relations have been studied in the BaO-CuOx system in the range of 25.0–45.0 mol % CuO at P(O2) = 21 kPa by visual polythermal analysis (VPA), X-ray phase analysis (XPA), differential thermal analysis (DTA), thermogravimetric analysis (TGA), chemical analysis (CA), X-ray microprobe analysis (XMEA), and electron diffraction (ED), with simultaneous elemental analysis (EA) by a transmission electron microscope (TEM). A discrete deviation of the 2.10, 2.08, 2.04, 2.02 (Ba/Cu) compositions from stoichiometry in the known Ba2CuO3 + δ oxides is found. New oxides of the 2.00, l.75, 1.66, 1.15 (Ba/Cu) compositions are revealed and their unit-cell parameters are determined. The phase diagram of the BaO-CuOx system is constructed, whose structure is considered as the total projection of phase states of the system at T = f(x) in CuOx.

On the thermal stability of the barium-copper oxide BaCuO2 at 900–1100°C in air

Phase relations in the 45.0–65.0 mol % CuO region of the BaO-CuOx system at P(O2) = 21 kPa have been studied by visual polythermal analysis (VPA), X-ray phase analysis (XPA), differential thermal analysis (DTA), thermogravimetric analysis (TGA), chemical analysis (CA), X-ray microprobe analysis (XMEA), and electron diffraction (ED) and elemental analysis (EA) in a transmission electron microscope (TEM). It is found that the investigated region of the diagram consists of several crystallization fields related to barium—copper oxides of cationic (Ba: Cu) compositions of 4: 5, 5: 6, 7: 8, 12: 13, and 24: 25 with the cubic structure of BaCuO2 oxide. They can be represented as a BamCum + nOy homologous series, where m = 3, 4, 5, …, n = l, 2. The 24: 25 oxide has the highest melting point in the studied region of the phase diagram. The BaCuO2 oxide does not exist in the subsolidus region under these conditions and does not have its own crystallization field.

Effect of the percentage of yttrium oxide on the phase composition of annealed samples of Y z Ba5Cu7O y and Y z Ba3Cu5O y composition

The phase composition of YzBa5Cu7Oy (1) and YzBa3Cu5Oy (2) samples with a variable percentage of yttrium up to the stoichiometric composition of the YnBamCum + nOy series is investigated by X-ray phase and elemental analyses, electron diffraction, and high resolution imaging in a transmission electron microscope at a temperature of 930°C in the crystallization field of a matrix oxide (Ba: Cu) of 5: 6 composition on the phase diagram of the BaO-CuOx system at P(O2) = 21 kPa. The substantial effect of yttrium oxide’s presence on the phase composition of both objects is found, providing evidence of a complex ionic equilibrium within the melt. The fine-domain oxide structure of the YBa2Cu3O6 tetragonal form, which is due to the coexistence of oxides of an YnBamCum+nOy homologous series of (Y: Ba: Cu) 235, 123, and 257 composition is revealed. The domain size for these phases is 20–50 Å. The domains are joined coherently along axis c.

Primary crystallization field of YnBamCum + nOy oxides with YBa2Cu3O6 tetragonal structure

The phase composition of specimens in the primary crystallization field of the YnBamCum + nOy oxide series with compositions of (Y:Ba:Cu) 235, 123, and 257 was investigated by means of X-ray powder diffraction, X-ray microprobe analysis, electron diffraction, and high resolution imaging in a transmission electron microscope. YnBamCum + nOy oxides have the YaBa2Cu3O6 tetragonal structure and can be represented in the general form as 123 oxides. It was found that the crystallization field of 123 oxides corresponds to the crystallization fields of the BamCum + nOy oxide series with the BaCuO2 cubic structure. These crystallization fields are located in the matrix phase diagram of the BaO-CuOx system at P(O2) = 21 kPa in the range of 50–90 mol % CuO and 910–1000°C. The 123 oxides are formed according to an intercalation mechanism with the participation of barium-copper oxide matrices with the composition (Ba: Cu) 3: 5, 2: 3, and 5: 7

Barium bismuth oxides with α-, γ-, and ɛ-Bi2O3 structures

Three new barium bismuth oxides have been synthesized containing 2.15–2.72 mol % BaO with the integer composition BaBi39O59.5, BaBi46O70, and BaBi40O61 and a monoclinic, cubic, and triclinic structure, respectively. These double oxides are, likely, derivatives of α-, γ-, and ɛ-Bi2O3 phases. The effects of the crucible material and surrounding atmosphere on the course of the synthesis of these new barium bismuth oxides are elucidated.

New barium bismuth oxides: BaBi4O7 and BaBi15O23.5

AbstractNew barium bismuth oxides have been synthesized under an argon atmosphere at 530 and 430°C, respectively: a Ba: Bi = 1 : 4 phase has a tetragonal perovskite structure, and a 1 : 15 phase has a rhombohedral structure. For the 1 : 4 phase, the unit cell parameters are a = 4.297(2) Å and c = 4.472(2) Å as determined by powder X-ray diffraction (XRD). Electron diffraction (ED) patterns show superstructure reflections with the vectors q1= 1/17[530], q2 = 1/17[3