CaO CuO Research Articles

Synthesis of a low-firing BaSi2O5 microwave dielectric ceramics with low dielectric constant

In this study, BaSi2O5 ceramics with an orthorhombic structure were synthesized by using a traditional solid-state method at a low temperature by doping with Li2O–B2O3–CaO–CuO (LBCC) glass. The phase composition, mechanism of low-temperature sintering, microwave dielectric properties, and changes in the mesophase during the heating of low-temperature sintered BaSi2O5 ceramics were examined by performing an X-ray diffraction analysis. A compact matrix of BaSi2O5 can be wetted by the liquid phase of the formed LBCC glass. Therefore, LBCC glass with different doping percentages can effectively reduce the sintering temperature of BaSi2O5. The microwave dielectric properties of BaSi2O5 ceramics sintered at 900 °C at 4 wt% of LBCC glass were determined: εr = 7.32, Q × f = 19,002 GHz, and τf = −35.8 ppm/°C. The chemical compatibility of the samples with Ag was studied at 4 wt% doping with LBCC glass, and the samples were fired for 4 h at 900 °C.

Estimation of Metal Drop Size on a Reducing Gas Bubble during Oxide Melt Bubbling

In this paper, we use the metal-phase formation model to estimate the drop size formed on individual bubbles of the reducing gas during the oxide melt bubbling. The model includes the following stages: the bubble formation upon gas injection into the melt, metal reduction on the bubble surface, and its drop concentration in the stern. We present equations that estimate the limiting sizes of a gas bubble ( $$R_{{\text{b}}}^{{{\text{cr}}}}$$ ) and a drop ( $$r_{{\text{d}}}^{{{\text{cr}}}}$$ ) moving in an oxide melt without defragmentation. The critical sizes of a gas bubble ( $$R_{{\text{b}}}^{{{\text{cr}}}}$$ ) moving in an oxide melt without defragmentation were calculated using the densities (ρ kg/m3) and surface tension (σ, mJ/m2) of B2O3–CaO and B2O3–CaO–CuO melts that are, respectively, described by the equations: σ1 = 87.0 + 0.242T , ρ1 = 3.26 × 103 – 0.91T, σ2 = 10.8 + 0.178T, ρ2 = 3.19 × 103 – 0.70T in the temperature range of 1373–1673 K. Depending on the temperature, the critical bubble radius varies from 0.047 to 0.053 m in the B2O3–CaO–CuO melt and 0.06–0.081 m in the B2O3–CaO melt. Depending on the CO amount introduced at various temperatures, the change in the copper oxide content in the B2O3–CaO–CuO melt was determined by calculating the thermodynamic equilibrium to describe the features of oxide melt bubbling by various reducing gases. Based on the obtained data, the copper amount produced from the interaction of Cu2O in the melt with a single CO bubble was calculated depending on the copper oxide content and the CO amount in the bubble. The correlation dependences of the drop size on the Cu2O content in the melt ( $${{C}_{{{\text{C}}{{{\text{u}}}_{{\text{2}}}}{\text{O}}}}}$$ , %), temperature (T, К), and the CO amount in the bubble (nCO, mol) were obtained by statistical data processing.

Preparation and dielectric properties of glass–ceramics in K2O–Al2O3–SiO2–CaO–CuO–TiO2 system

Glass–ceramics containing CaCu3Ti4O12(CCTO) crystalline phase were successfully prepared by air-quenching K2O–Al2O3–SiO2–CaO–CuO–TiO2 melts followed by heat treatment. X-ray diffraction, scanning electron microscopy and dielectric spectroscopy were used to characterize the samples. The results indicate that the as-synthesized samples are well crystallized upon the heat treatment. The main crystalline phases are KAlSi2O6, CCTO, CaTiO(SiO4), TiO2 and Cu2+1O. The dielectric constants of the as-synthesized samples increase with the total contents of CaO, CuO, TiO2. However, the dielectric constants of the heat treated samples is related to the formed CCTO crystalline phase, whose content is influenced by the glassy phase in the as-synthesized sample or re-melting of the KAlSi2O6 phase during the heat-treatment. The heat treated sample having the highest amount of CCTO phase shows the largest dielectric constant of 38. The dielectric losses (100 kHz, room temperature) of the samples are relatively smaller than the reported data in the literature.

Combined calcium looping and chemical looping combustion cycles with CaO–CuO pellets in a fixed bed reactor

The feasibility of using integrated CaO/CuO-based pellets in combined calcium and chemical looping cycles in a fixed bed was investigated with emphasis on CO2 capture performance. Three types of pellets were tested, namely; integrated core-in-shell CaO/CuO-based pellets; integrated homogeneous CaO/CuO-based pellets; and mixed CaO-based pellets and CuO-based pellets. Redox cycles consisted of oxidation/carbonation at 650°C in 15% CO2; 4% O2, and N2 balance, and reduction/calcination at 850°C in a CO/H2 mixture. The results showed that mixed pellets exhibited the highest CO2 uptakes of 0.11g CO2/g bed in the first cycle and 0.07g/g after 11 cycles (corresponding to CaO conversions of 32.1% and 19%, respectively). This enhanced performance was attributed to the significantly higher pore volume and surface area in the calcined CaO-based pellets, which were superior to those of integrated CaO/CuO-based pellets. The reduction of CuO to Cu2O was found to be partially irreversible, with ∼45% of copper oxide in the pellets in the form of Cu2O despite the excess O2 in the oxidizing environment. It was also noted that cycled core-in-shell pellets were the most susceptible to fragmentation, indicating the low mechanical strength of these pellets. It was concluded that combined calcium and chemical looping cycles in a fixed bed system is a feasible process providing suitable pellets are used. Incorporating CuO in CaO-based pellets reduces the porosity of the pellets, thus compromises CO2 uptake. Among the three groups of pellets, mixed pellets are the most promising for CaL–CLC processes due to their better performance, easier manufacturing, and better quality control than integrated pellets.

Subsolidus Phase Relationship in the CaO–CuO–TiO2 Ternary System at 950°C in Air

The subsolidus phase relationship in the CaO–CuO–TiO2 ternary system at 950°C in air was investigated. Total 26 samples having various nominal compositions were prepared by the solid‐state reaction at 950°C in air, and their equilibrium phases were analyzed by powder X‐ray diffraction (XRD). The CaCu3Ti4O12 phase exhibits variable stoichiometry and forms as the Ca1−xCu3+xTi4O12‐type (−0.019 ≤x ≤0.048) solid solution at 950°C in air. On the basis of our results and previous reports on the binary phase diagrams, the subsolidus phase diagram of the CaO–CuO–TiO2 ternary system could be constructed at 950°C in air.

Non-stoichiometry in “CaCu3Ti4O12” (CCTO) ceramics

A combined powder X-ray lattice parameter and ceramic impedance spectroscopy study is presented on materials within the CaO–CuO–TiO2 ternary phase diagram. Several compositions containing CaCu3Ti4O12 (CCTO) and small amounts of secondary phases such as TiO2, CaTiO3 and CuO are analysed and two different defect mechanisms are identified as the cause of the non-stoichiometry in CCTO. The first mechanism involves a variation in the Cu content, which explains the large differences in the intrinsic bulk and extrinsic grain boundary (GB) resistance, and the formation of the ceramic internal barrier layer capacitor (IBLC) structure. The second mechanism is associated with Ca–Cu anti-site disorder causing an unusually high intrinsic bulk permittivity above that predicted from Clausius–Mossotti calculations.

Structural studies of copper-containing multicomponent glasses from the SiO2–P2O5–K2O–CaO–MgO system

Multicomponent glasses from the SiO2–P2O5–K2O–MgO–CaO–CuO system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of CuO and P2O5 addition on the structure of glasses was evaluated by FTIR, Raman, 31P, and 29Si MAS NMR spectroscopies. The studies showed that the Cu2+ ions displacing Ca2+ ions and Mg2+ ions in the structure of glass prefer to associate with the phosphorus Q1 species, forming the Q0 species with chemically stable POCu bonds. This is accompanied by the reduction of the degree of polymerization of the phospho-oxygen sub-network, with a simultaneous increased degree of polymerization of the silico-oxygen sub-network of the silicate–phosphate glasses.

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO2–P2O5–K2O–MgO–CaO–CuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P–O–Cu bonds formation. Degree of changes of T g, ∆c p, and time of relaxation values were higher in glasses with higher content of P2O5 and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.

Giant dielectric constant response of the composites in ternary system CuO–TiO 2–CaO

The subsolidus phase relations of the ternary system CuO–TiO 2–CaO sintered at 950 °C in air have been determined by powder X-ray diffraction method. Only one ternary compound CaCu 3Ti 4O 12 was found in this system. From room-temperature dielectric property mapping at 10 kHz, a giant dielectric constant ( ε r >10 4) was observed for most of the ceramic composites in the CuO-rich region and in the region along the CaO–CuO binary line. The composites in the CaCu 3Ti 4O 12-rich region were found to give a comparable giant dielectric constant when sintered at 1050 °C. The particular microstructure of larger grains with predominant phase surrounded by smaller grains with the secondary phases was found in such composites with a high dielectric constant. The relations between structures and dielectric properties were investigated. An internal barrier layer capacitance effect is the most probable mechanism to explain this particular dielectric behavior.

Thermodynamic calculation of the BiO 1.5–CaO–CuO x system

The BiO 1.5–CaO–CuO x system is by far the simplest of the four ternary systems forming the BiO x –SrO–CaO–CuO x system where the superconducting phases Bi 2Sr 2CaCu 2O 8+ δ and Bi 2Sr 2Ca 2Cu 3O 10+ δ are found. The only solution phase extending into the system is the liquid phase. Using a single interaction parameter the experimentally determined [M.-L. Carvalho et al., Physica C 336 (2000) 1] eutectic temperature at 1024 K in 1 bar O 2 could be fitted and the complete phase diagram calculated.

Thermodynamic assessment of the BiO x–SrO–CaO system

The BiO x –SrO–CaO system is the most complex of the four ternary systems forming the BiO x –SrO–CaO–CuO x system where the superconducting phases Bi 2Sr 2CaCu 2O 8+ δ and Bi 2Sr 2Ca 2Cu 3O 10+ δ are found. The BiO x –SrO–CaO system has received relatively little attention since it does not contain any superconducting phases itself. Several of the phases in this system appear during processing of superconductors, though. Using the Calphad approach, we have assessed the experimental data of this system and optimised a set of thermodynamic parameters from which the phase diagram and any thermodynamic property can be calculated. The experimental data available are quite scattered and often contradictory, but the thermodynamic description presented here is consistent with most of what is known about this system.

Subsolidus phase relations and crystal structure of compounds in the PrO x–CaO–CuO system

The subsolidus phase relations of the PrO x –CaO–CuO pseudo-ternary system sintered at 950–1000°C have been investigated by X-ray powder diffraction. In this system, there exist one compound Ca 10Pr 4Cu 24O 41, one Ca 2Pr 2Cu 5O 10-based solid solution, seven three-phase regions and two two-phase regions. The crystal structures of Ca 10Pr 4Cu 24O 41 and Ca 2Pr 2Cu 5O 10-based solid solution have been determined. Compound Ca 10Pr 4Cu 24O 41 crystallizes in an orthorhombic cell with space group D 2 h 20− Cccm, Z=4. Its lattice parameters are a=11.278(2) Å, b=12.448(3) Å and c=27.486(8) Å. The crystal structure of Ca 2Pr 2Cu 5O 10-based solid solution is an incommensurate phase based on the orthorhombic NaCuO 2 type subcell. The lattice parameters of the subcell of the Ca 2.4Pr 1.6Cu 5O 10 are a 0=2.8246(7) Å, b 0=6.3693(5) Å, c 0=10.679(1) Å, and those of the orthorhombic superstructure are with a=5 a 0, b= b 0, c=5 c 0. The Ca 2.4Pr 1.6Cu 5O 10 structure can also be determined by using a monoclinic supercell with space group C 2 h 5− P2 1/ c, Z=4, a=5 a 0, b= b 0, c=c 0/ sin β and β=104.79(1)° or 136.60(1)°, V=5 a 0 b 0 c 0.

Subsolidus phase relations of the constant copper oxide content (50 mol%) section in the PrO 11/6–BaO–CaO–CuO system at 950 °C

Subsolidus phase relations of the constant copper oxide content (50 mol%) section in the PrO 11/6–BaO–CaO–CuO system at 950 °C in air are investigated by means of X-ray diffraction analyses. The phase relations consist of 1 single-phase region, 1 two-phase region, 2 three-phase regions and 6 four-phase regions. Mutual substitutions among Pr, Ba and Ca in the Pr123 structure were studied in detail. The result indicates that Ba ions can be replaced exclusively by Pr ions, but not by Ca ions, whereas Ca ions can partially occupy the sites of Pr ions. The ionic radius plays a more important role than the chemical property for substitution among Pr, Ba and Ca ions in the Pr123 structure.

Subsolidus phase relations and crystal structures of R–Ca–Cu–O ( R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R 2O 3–CaO–CuO ternary systems ( R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca 14− x R x Cu 24O 41 ( x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca 2+ x R 2− x Cu 5O 10 ( R=Nd, Sm, Gd, Tm) with a wide composition range Δ x of about 0.6. The compound Ca 14− x R x Cu 24O 41 possesses a layered orthorhombic structure and is isostructural to Sr 14− x Ca x Cu 24O 41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca 2+ x R 2− x Cu 5O 10 solid solution is isostructural to Ca 2+ x Y 2− x Cu 5O 10, the structure of which is based on an orthorhombic “NaCuO 2-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.

The CaO–CuO–TlO 1.5 system and its key role in the formation of the Tl-based superconductors

It has been shown recently that the formation of Tl 2Ba 2Ca 2Cu 3O z is conditioned by an equilibrium plane with the Tl-rich limit of the (Ca,Tl) 1− x CuO 2 solid solution as one of the apices. The parent phase for the latter solid solution is the binary compound Ca 0.80CuO 1.93. We report here on the phase relations in the CaO–CuO and the CaO–CuO–TlO 1.5 systems. The emphasis is also put on the thermodynamic stability and the crystallographic properties of Ca 0.80CuO 1.93 (space group P2/c, a=10.9456(4) Å, b=6.3192(2) Å, c=16.8408 Å and β=104.952(2)°). The kinetics for phase formation and decomposition have been studied. In particular, we show that the decomposition reaction into Ca 2CuO 3 and CuO which occurs at 870 °C in p(O 2)=1 bar and at 720 °C in vacuum, is rate limited by a two-dimensional process consistent with structural considerations and has an activation energy of 656 kJ/mol.

CaO–CuO system at high oxygen pressure: bulk synthesis and transport properties of Ca 14Cu 24O 41

CaO–CuO system has been investigated at high oxygen pressure. Only two ternary compounds, Ca 0.83CuO 2 and Ca 14Cu 24O 41, were found to be stable at P(O 2)=500 bar. Ca 14Cu 24O 41 has been synthesized as a bulk phase for the first time. The formation of this phase occurs only in a very narrow range of temperature and oxygen pressure. Resistivity measurements at high pressure from 3 to 8.5 GPa show superconducting transition in the whole range of pressures. Magnetic properties of this compound at ambient pressure have been also studied.

Phase Diagram Studies in the System Tl2O3-BaO-CaO-CuO-Ag

The phase relations within the system Tl2O3–BaO–CaO–CuO including Ag have been studied with emphasis on the high-temperature superconducting phases TlBa2Ca2Cu3O8.5 (1223 phase), Tl2Ba2Ca2Cu3O10 (2223 phase), TlBa2CaCu2O6.5 (1212 phase), and Tl2Ba2CaCu2O8 (2212 phase) at 890°C in an oxygen atmosphere. 1223 has been found to be in equilibrium with a liquid phase that is Tl poor. 2223 and 2212 exhibit varying Tl/(Ba + Ca) ratios. The three-phase field 1223 + 2223 + 2212 has been identified. The results of this study emphasize that multiphase samples can be prepared which consist of three superconducting phases, each exhibiting a critical temperature of 100 K or above.

The influence of Ag on Bi-2212 and Bi-2223

The phase relations within the system Bi 2O 3PbOrOCaOCuO including Ag has been studied with emphasis on the superconducting phases (Bi,Pb) 2Sr 2Ca 2Cu 3O 10 (2223 phase) and Bi 2Sr 2CaCu 2O 8 (2212 phase). The onset temperatures of the peritectic melting of 2223 and 2212 were observed to be decreased by about 20–30 °C when Ag is present. In addition, the solid solubility of Sr in 2212 and Pb in 2223 is affected by Ag.

Phase equilibria in the system Tl 2O 3BaOCaOCuOAg

The phase relations within the system Tl 2O 3BaOCaOCuO including Ag has been studied with emphasis on the high temperature superconducting phases TlBa 2Ca 2Cu 3O 8.5 (1223 phase), Tl 2Ba 2Ca 2Cu 3O 10 (2223 phase), TlBa 2CaCu 2O 6.5 (1212 phase), and Tl 2Ba 2CaCu 2O 8 (2212 phase) at 890 °C in oxygen atmosphere. 1223 has been found to be in equilibrium with a liquid phase which is Tl poor.

Liquidus phase equilibria in portions of the BSCCO system

This paper summarizes a systematic investigation of the phase equilibria in the quaternary BiO 1.5SrOCaOCuO system (BSCCO). The study combines our completed work on subset binaries and ternaries and experiments in the quaternary system, focusing on the small volume of the quaternary where the primary phase volumes of ternary and quaternary BSCCO phases exist. Known phase relations and conducted experiments within the BSCCO quaternary support the findings of this paper.