The analytic equations for the Gibbs energy of Nd-Ba-Cu-O system phases obtained earlier were used to calculate the phase diagrams of the Ba0.5Cu0.5O-Nd0.5Cu0.5O section at oxygen partial pressures of 0.21 and 1 bar. For p(O2)= 0.21 bar, the coordinates of the nonvariant system points, the projection of the liquidus surface, and the phase diagram of the Nd1 + xBa2 ? xCu3O6 + z compound in the subsolidus region were determined. 相似文献
The available experimental data were used to construct thermodynamic models of Nd-Ba-Cu-O system phases. The coordinates of the nonvariant points of this system were determined, and the phase diagram for the Nd1 + xBa2 ? xCu3O6 + z(x = 10?4) compound was calculated. 相似文献
During attempts to synthesize lanthanoid(III) fluoride oxoselenates(IV) with the simple composition MF[SeO3], not only Pr3F[SeO3]4, but also Pr5F[SiO4]2[SeO3]3 appeared as pale green crystalline by‐products in the case of praseodymium. Pr5F[SiO4]2[SeO3]3 crystallizes triclinically in space group P$\bar{1}$ (no. 2) with a = 701.14(5), b = 982.68(7), c = 1286.79(9) pm, α = 70.552(3), β = 76.904(3), γ = 69.417(3)° and Z = 2. The five crystallographically different Pr3+ cations on the general positions 2i show coordination numbers of eight and nine. [(Pr1)O8]13– and [(Pr2)O8]13– polyhedra are connected to$\bar{1}$ {[(Pr1, 2)2O12]18–} chains along the [100] direction. [(Pr3)O7F]12–, [(Pr4)O8F]14– and [(Pr4)O8F]14– polyhedra generate [F(Pr3, 4, 5)3O19]30– units about their central F– anion in triangular Pr3+ coordination. These units form $\bar{1}$ {[F(Pr3, 4, 5)3O16]24–} strands, again running parallel to [100]. Their alternating connection with the $\bar{1}$ {[(Pr1, 2)2O12]18–} chains results in $\bar{1}$ {[Pr5O20F]26–} sheets parallel to the (001) plane. Like in the already known related compound Er3F[SiO4][SeO3]2, a three‐dimensional network $\bar{1}$ {[Pr5O17F]20–} is achieved without the contribution of both the tetravalent silicon and selenium components. However, two Si4+ and three Se4+ cations forming tetrahedral [SiO4]4– and ψ1‐tetrahedral [SeO3]2– units with all O2– anions guarantee the charge balance. The formation of Pr5F[SiO4]2[SeO3]3 was observed when praseodymium sesquioxide (Pr2O3: in‐situ produced from Pr and Pr6O11 in a molar ratio of 3/11:4/11),praseodymium trifluoride (PrF3) and selenium dioxide (SeO2) in 1:1:3 molar ratios were reacted with CsBr as fluxing agent for five days at 750 °C in evacuated fused silica (SiO2) ampoules. 相似文献
Chemical Transport in the System Mn? O in Consideration of the Oxygen Coexistence Pressure (I) The chemical transport of the coexistent phases Mn2O3? Mn3O4 and Mn3O4? MnO with Cl2, Br2, I2, HCl, HBr, and HI was analysed thermodynamically and experimentally. The mentioned transport agents are able to transport the following phases:
The system CuO/In2O3/P2O5 has been investigated using solid state reaction between CuO, In2O3 and (NH4)2HPO4 in silica glass crucibles at 900 °C. The powder samples were characterized by X‐ray diffraction, thermal analysis and FT‐IR spectroscopy. Orange single crystals of the new quaternary phase were achieved by the process of crystallization with mineralizers in sealed silica glass ampoules. They were then analyzed with EDX and single‐crystal X‐ray analysis in which the composition Cu8In8P4O30 with the triclinic space group P$\bar{1}$ (No 2) with a = 7,2429(14) Å, b = 8,8002(18) Å, c = 10,069(2) Å, α = 103,62(3)°, β = 106,31(3)°, γ = 101,55(3)° and Z = 1 was found. The three‐dimensional framework consists of [InO6] octahedra and distorted [CuO6] octahedra, overcaped [InO7] prisms and [PO4] tetrahedra, also trigonal [(CuIn)O5] bipyramids and distorted [(CuIn)O6] octahedra, where copper and indium are partly exchanged against each other. Cu8In8P4O30 exhibits an incongruent melting point at 1023 °C. 相似文献
A structural investigation is reported of polymorphs of Ga2O3 that, despite much interest in their properties, have hitherto remained uncharacterised due to structural disorder. The most crystalline sample yet reported of γ‐Ga2O3 was prepared by solvothermal oxidation of gallium metal in ethanolamine. Structure refinement using the Rietveld method reveals γ‐Ga2O3 has a defect Fd$\bar 3$ m spinel structure, while pair distribution function analysis shows that the short‐range structure is better modelled with local F$\bar 4$ 3m symmetry. In further solvothermal oxidation reactions a novel gallium oxyhydroxide, Ga5O7(OH), is formed, the thermal decomposition of which reveals a new, transient gallium oxide polymorph, κ‐Ga2O3, before transformation into β‐Ga2O3. In contrast, the thermal decomposition of Ga(NO3)3?9 H2O first forms ε‐Ga2O3 and then β‐Ga2O3. Examination of in situ thermodiffraction data shows that ε‐Ga2O3 is always contaminated with β‐Ga2O3 and with this knowledge a model for its structure was deduced and refined—space group P63mc with a ratio of tetrahedral/octahedral gallium of 2.2:1 in close‐packed oxide layers. Importantly, thermodiffraction provides no evidence for the existence of the speculated bixbyite structured δ‐Ga2O3; at the early stages of thermal decomposition of Ga(NO3)3?9 H2O the first distinct phase formed is merely small particles of ε‐Ga2O3. 相似文献
In the work presented here, the way of obtaining the phase with general formula Co3+1.5xCr2–x(VO4)4 (0 ≤ × < 0.4) is demonstrated. A new phase is detected in CrVO4 - Co3V2O8 that is formed in one of the intersection of the ternary CoO - V2O5 - Cr2O3 system. Monophasic Co3Cr2(VO4)4 (Co3+1.5xCr2−x(VO4)4, where × = 0) was obtained from both a mixture comprising CrVO4 and Co3V2O8 as well as from the mixture of CoV2O6 with CoCr2O4. The Co3+1.5xCr2−x(VO4)4 is isotypic with the those demonstrating the lyonsite-type structure. The temperature of melting for the new compound was
established using the DTA methods.
相似文献
On Hexagonal Perovskites with Cationic Vacancies. XXIV. Rhombohedral 9 L Stacking Polytypes in the Systems Ba3W M □O9?x/2□x?2 with MV = Nb, Ta In the system Ba3WNb□O9?x/2□x/2 stacking polytypes of rhombohedral 9 L type (sequence (hhc)3; space group R3 m) can be prepared with ~1/3 ? × ? 2. For x = 2(Ba3Nb2□O8□) two modifications are formed. In the corresponding Ta system the phase with is reduced to a smaller region with x ? 1/3. 相似文献
Chemical Transport in the System Mn? O in Consideration of the Oxygen Coexistence Pressure. II The chemical transport of the coexistent phases Mn2O3? Mn3O4 and Mn3O4? MnO with TeCl4 and SeCl4 was analysed thermodynamically and experimentally. This two transport agents are able to transport the following phases:
On the Chemical Transport of Cr2O3 with Br2 and CrBr3/Br2 — Experiments and Model Calculations for Participation of CrOBr2,g and CrO2Br2,g Gaseous chromium oxybromides that were unknown up to now cause the migration of the starting material Cr2O3 in the temperature gradient from T2 = 1000°C to T1 = 900°C when Br2 or Br2/CrBr3 respectively is added. Model calculations show that under the influence of H2O (from the wall of the silica ampoule) or O2 (from a homogenous equilibrium between H2O/Br2) the transport takes place via the oxybromide CrO2Br2 of the hexavalent chromium (eq. (1) and (2)). For thermodynamical reasons eq. (2) seems to be more favourable. At higher temperature the less oxygen containing gas species CrOBr2,g has also to be taken into account if H2O is excluded. An addition of CrBr3 lowers the partial pressure of oxygen (and of H2O as well) in the system Cr2O3/Br2. Under this conditions CrOBr2,g becomes an important species for the transport of the solid phase (eq. (4)) and CrBr4,g has to be considered as transport agent. Estimated values of the enthalpies of formation were fixed more precisely by thermodynamic model calculation. For CrOBr2,g (system Cr2O3/CrBr3/Br2) ΔfH°298 = ?70 kcal/mol and for CrO2Br2 (Cr2O3/Br2) ΔfH°298 = ?107,4 kcal/mol was found. The estimated limits of error for the enthalpies of formation given for both oxybromides are smaller than ±5 kcal/mol. 相似文献
In this study the formation of chromium substituted YBa2Cu4O8 (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa2(Cu1−xCrx)4O8 ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding
metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist
the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction
(XRD) and resistivity measurements. It was determined that doping the YBa2Cu4O8 phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products. 相似文献
Copolymerizations of vinylidene fluoride (VDF) and hexafluoropropene (HFP) were carried out in homogeneous phase with supercritical carbon dioxide up to complete VDF conversion using conventional peroxide initiators. The HFP monomer feed ratios, fHFP, were varied between 0.65 and 0.20. Depending on fHFP amorphous or semi‐crystalline copolymers were obtained. fHFP also determines the minimum pressure required to allow for homogeneous phase reactions. For example, HFP‐rich copolymerizations in 70 wt.‐% CO2 at 100 °C require a pressure of around 500 bar. Further, bulk copolymerizations in homogenous phase were feasible for fHFP = 0.65 at 900 bar up to complete VDF conversion. Copolymerizations in the presence of perfluorinated hexyl iodide carried out at 75 °C gave access to low dispersity polymers. Due to homogeneous phase conditions the use of any surfactants or fluorinated cosolvent is avoided.
The crystal structure and stability of Ba4CaCu3O8+δ have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065 K in p(O2)=1 bar and decomposes according to the eutectoid reaction Ba4CaCu3O8+δ+x O2⇒Ba2CuO3.4+CaO+2BaCuO2. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba4CaCu3O8+δ can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, , δ=0.68, Z=2, Rwp=2.5%, RBragg=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O2)<10−6 bar), Ba4CaCu3O8+δ is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, , , δ=-0.81, Z=2, Rwp=2.8%, RBragg=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba4CaCu3O8+δ is also discussed. 相似文献
Structural mechanisms of formation of low-symmetry phases of cyanospinels are described in terms of the phenomenological theory
of phase transitions. These are examined for transitions from a spinel structure to two cubic
and four rhombohedral
phases, induced by automorphic irreducible representations 9-2 and 9-3. Atomic coordinates and the symmetry types of occupied
positions in asymmetric phases are determined. Criteria for discrimination between the two
as well as between the four
phases are formulated. The structures of complex cyanides Tl2Zn(CN)4
, K2Zn(CN)4, K2Hg(CN)4, and Rb2Hg(CN)4
are calculated. The displacements and irreducible representations inducing transitions from spinel structures to these phases
are determined.
Novocherkassk State Technological University. Translated fromZhumal Struktumoi Khimii, Vol. 35, No. 5, pp. 41–49, September–October, 1994.
Translated by L. Smolina 相似文献
A Contribution on the Crystal Structure of CuYW2O8, CuHoW2O8, and CuYW2O8 Single crystals of (I) CuY2O8, (II), CuHoW2O8, and (III) CuYbW2O8 were prepared and investigated by X-ray technique. (I) crystallizes with triclinic symmetry, space group C? P1 (a = 5.939 Å, b = 6.042 Å, c = 5.025 Å; α = 112.30°, β = 111.77°; Z = 1). (II) and (III) belong to monoclinic symmetry, space group C? P2/n (II) (a = 10.045 Å, b = 5.808 Å, c = 5.021 Å; β = 94.38°; z = 2 (III) a = 9.948 Å, b = 5.824 Å, c = 5.008 Å; β = 93.36°; Z = 2). The crystal structures will be discussed with respect to other to copper rare earth tungstates. 相似文献
Crystal Chemistry of the Lead Lanthanide Oxoaluminates. On Pb2HoAl3O8 and Pb2LuAl3O8 . Single crystals of (I) Pb2HoAl3O8 and (II) Pb2LuAl3O8 were prepared by flux technique and investigated by X-ray methods. It crystallizes with cubic symmetry, space group O–P42/n 3 2/m, (I): a = 9.4164(13) Å, (II): a = 9.3486(8) Å, Z = 4. The new structure type shows AlO4 tetrahedra, LnO8 hexagonal bipyramids and one sided coordinated Pb2+ within heterocubane units. The crystal chemical relationships to other lead oxides containing heterocubane Pb4O4 units are discussed. 相似文献
Regioselectively ethylated celluloses, 2‐O‐ ( 1 ), 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3 ) celluloses were synthesized via ring‐opening polymerization of glucopyranose orthopivalate derivatives. The number‐average degrees of polymerization (DPns) of compounds 1 and 2 were calculated to be 10.6 and 49.4, respectively. Three kinds of compound 3 with different DPns were prepared: DPns = 12.9 ( 3‐1 ), 60.3 ( 3‐2 ), and 36.1 ( 3‐3 ). The 2‐O‐, 3‐O‐, and 6‐O‐ethylcelluloses were soluble in water, confirmed by NMR analysis. Furthermore, the 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3‐2 ) celluloses showed thermo‐responsive aggregation behavior and had a lower critical solution temperature (LCST) at about 40 °C and 70 °C, respectively, based on the results from turbidity tests and DSC measurements. The 6‐O‐ethyl‐cellulose ( 3‐3 ) with DPn = 36.1 and DPw = 54.6 showed gelation behavior over approx 70 °C, whereas the 6‐O‐ethyl‐celluloses 3‐1 and 3‐2 with lower and higher molecular weight, such as DPns 12.9 and 60.3, did not show gelation behavior at this temperature. It was revealed that the position of ethyl group affected the phase transition temperature. According to our experiments, the 3‐O‐ethyl and 6‐O‐ethyl groups along the cellulose chains caused the thermo‐responsive property of their aqueous solutions. The appropriate DP of the regioselective 6‐O‐ethyl‐cellulose existed for gelation of the aqueous solution.
The system CuO‐Fe2O3‐P2O5 has been investigated by means of the solid state reaction between CuO, Fe2O3 and (NH4)2HPO4 in quartz crucibles at 900 °C. The powder samples were characterized by X‐ray diffraction, IR spectroscopy and TG/DTA. Single crystals of a new quaternary phase Cu8Fe2P4O21 were achieved by cooling from the melt of the compound in a sealed, evacuated quartz ampoule. Cu8Fe2O5(PO4)4 crystallizes in the monoclinic space group C2/m (No 12) with a = 15.9733(8) Å, b = 5.9438(3) Å, c = 9.5530(5) Å, β = 113.76(1)°, Z = 2. The three‐dimensional framework consists of [FeO6] octahedra, three different [CuO5] polyhedra and [PO4] tetrahedra. Cu8Fe2P4O21 exhibits an incongruently melting point at 945 °C. 相似文献