Peritectic Decomposition Temperature Research Articles

Essential role of liquid phase on melt-processed GdBCO single-grain superconductors

We systematically investigated the role of additional liquid source (LS) which creates a liquid-rich nucleation environment and influences the growth kinetic energy. It enables a significant decrease in maximum processing temperature (Tmax) even close to the peritectic decomposition temperature (Tp), hence optimizing the distribution and size of the Gd2BaCuO5 (Gd211) particles. By exploiting this combined LS and low Tmax (LS+LTmax) growth method, the performance of GdBa2Cu3O7-δ (GdBCO) single-grain superconductors has been greatly improved. Therefore, the maximum trapped magnetic fields reach 0.746 T and 1.140 T for the 18- and 25-mm-diameter samples at 77 K. Meanwhile, superior flux pinning performance has been observed at the growth section boundaries (GSBs) with a decreased density of Gd211 particles in the LS+LTmax samples. These results indicate that the LS+LTmax technology can fabricate high-performance single-grain superconductors with improved reliability which is considered important for engineering applications.

Phase transformations in WC-Cr3C2-Ni thermal spray coatings under low, medium and high thermal input: Part 1 – Feedstock and as-sprayed coating characterisation

Conventionally, bulk WC and Cr3C2-based carbide compositions have been used independently of each other. However, recent investigations have begun to explore combining these carbides together within the same composite/hard metal coating system. This work explored the diversity of phases produced in the coatings from a 42 wt% WC-42 wt% Cr3C2–16 wt% Ni powder sprayed under “low”, “medium” and “high” thermal input conditions using high velocity oxygen-fuel (HVOF), an argon‑helium (ArHe) plasma and an argon‑hydrogen (ArH2) plasma respectively. During spraying, the Ni binder melted, leading to variations in the extent of carbide dissolution and peritectic decomposition as a function of thermal input. Low thermal input, typified by the HVOF technique, led to preferential dissolution/decomposition of the Cr3C2 grains into the melt, while retaining more of the higher melting point WC grains. The coating was dominated by a supersaturated Ni phase, along with the retained carbides. High thermal input, typified by the ArH2 plasma, was postulated to exceed the peritectic decomposition temperature of WC. The coating consisted of a supersaturated Ni alloy, along with the metastable phases WC1-X and β-W2C. No metastable Cr-carbides formed in any of the coatings. The mechanism of coating phase formation is discussed.

Phase relations, structure, properties and DFT study of compounds in the Sc-rich part of the systems Sc-{Mn,Fe,Co,Ni}-Ga

Phase relations, structure, properties and DFT study of compounds in the Sc-rich part of the systems Sc-{Mn,Fe,Co,Ni}-Ga

Critical assessment and thermodynamic modeling of the Al–C system

The Al–C system is the backbone of wide variety of applications in multicomponent systems, and was therefore studied intensively. Yet, considerable disagreements remain in the reported data, and the phase equilibria in the binary system as well as the standard enthalpy of formation of Al4C3 are still debated. In order to establish a reliable thermodynamic description of the Al–C system a thorough and critical assessment of the literature was conducted. The data on the solubility of carbon in liquid Al and on the thermodynamic properties of Al4C3 were assessed, and the peritectic decomposition temperature of Al4C3 was confirmed at 2425 ± 15 K by thermal analysis. Thermodynamic modeling of the Al–C system is provided and compared to previous works. The proposed description was found to be more robust and to carry more physical meaning than any previous modeling of the system, which imply an easier extrapolation of the binary into higher-order systems.

Mechanical Properties of Superconducting (Gd,Y)BaCuO Large Single-Grain Material Fabricated by RE Compositional Gradient Technique

In order to investigate the mechanical properties of a (Gd,Y)BaCuO large single-grain bulk material, bending tests were carried out at room temperature for the specimens cut from the bulk material. A precursor, which consisted of three regions with different Gd and Y contents, was used for the fabrication of the large single-grain bulk material in order to overcome the undesirable nucleation apart from the seed crystal. The precursor was prepared such that Y content increased with increase in the distance from the center, where the seed crystal was placed, to decrease the peritectic decomposition temperature. Two types of bending test specimens were cut from the bulk material—the specimens that included the interface between two regions with different Gd and Y contents and the specimens that did not include the interface. Although the bending strength data of the specimens that did not include the interface scattered widely in comparison with the specimens that included the interface, the average bending strength values of these specimens were similar to each other. This result demonstrates that the interface does not cause the deterioration of the mechanical properties of the whole bulk material.

Synthesis and Characterization of Ag2MnSnS4, a New Diamond‐like Semiconductor

Phase pure Ag2MnSnS4 was synthesized from the elements using standard high‐temperature solid‐state methods. Its crystal structure was solved from single‐crystal X‐ray diffraction data collected from a pseudo‐merohedrally twinned crystal as well as by Rietveld refinement of X‐ray powder diffraction data. Ag2MnSnS4 crystallizes in the monoclinic space group Pc (no. 7) with the unit cell parameters a = 6.651(1), b = 6.943(1), c = 10.536(2) Å, β = 129.15(1)°, V = 337.3(1) Å3, and Z = 2. The tetrahedraly compound crystallizes in a superstructure of the wurtzite type and the tetrahedra volumes are in good agreement with the model for diamond‐related compounds derived from the wurtzite structure type. The red semiconductor Ag2MnSnS4 has an optical bandgap of Eg = 2.0 eV and is stable up to its peritectic decomposition temperature of approximately 700 °C. Ag2MnSnS4 is a Curie–Weiss paramagnet with an experimental magnetic moment of μexp = 5.4(1) μB per manganese atom. Antiferromagnetic ordering is detected at a Néel temperature of TN = 8.8(1) K. 119Sn Mößbauer spectra at 78 K underline the single tetrahedrally coordinated SnIV site (δ = 1.34(1) mm·s–1). The 6 K spectrum (magnetically ordered state) reveals a small transferred magnetic hyperfine field of 1.02(1) T.

Process Technology and Superconducting Properties of Bulk HTS With Multi-RE Elements

A series of REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (RE123)/Ag bulk superconductors with multi-RE elements at the RE site, were prepared by top-seeded melt growth. By employing the differential thermal analysis, we carefully adjusted the peritectic decomposition temperature ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) by changing the ratio of the two RE123 compositions to meet the requirements of the cold-seeding process. The superconducting properties, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and the flux trapping performance were evaluated after achieving the growth of the single grains. The microstructure was also observed. A relatively low growth temperature range depressed the LRE-Ba substitution, which was effective to suppress the probable RE211 coarsening. By employing ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> chemical doping, the flux pinning property was further improved under both zero-field and in-field, and the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was enhanced without reducing <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

Study of the In–S phase diagram using spectrophotometric characterization of equilibria between hydrogen and indium sulfides

We have developed and put in practice a spectrophotometric procedure for hydrogen sulfide determination to study the phase diagram of the In–S system using hydrogen as an auxiliary component. Elemental analysis of the hydrogen-containing vapor phase allows the principal thermodynamic properties of the indium sulfides in equilibrium with the vapor phase to be assessed in wide temperature and composition ranges. Our results confirm the existence of a narrow two-phase field between In3−xS4 and In2S3′ (low-temperature phase), which is bounded from above by the peritectic decomposition temperature of In2S3′ (about 415°C). We have determined the temperature-dependent sulfur (S2) vapor pressure over condensed indium sulfides. For the equilibria studied in greatest detail, the present results correlate well with mass spectrometry data for indium sulfides.

Refinement of the In-S phase diagram using spectrophotometric characterization of equilibria between hydrogen and indium sulfides

A spectrophotometric procedure for hydrogen sulfide determination has been developed and utilized to study the phase diagram of the In-S system using hydrogen as an auxiliary component. Elemental analysis of the hydrogen-containing vapor phase allows the principal thermodynamic properties of the indium sulfides in equilibrium with the vapor phase to be assessed in wide temperature and composition ranges. Our results confirm the existence of a narrow two-phase field between In3−x S4 and In2S′3 (low-temperature phase), which is bounded from above by the peritectic decomposition temperature of (about 415°C). We have determined the temperature-dependent sulfur (S2) vapor pressure over condensed indium sulfides. For the equilibria studied in greatest detail, the present results correlate well with mass spectrometry data for indium sulfides.

Growth and investigation of SmBCO/Ag single grain bulk for batch production of Sm123 seed crystals

Using NdBa 2Cu 3O y (Nd123) bulk material as a seed, we report a success in the melt-textured growth of SmBCO/Ag bulks by cold-seeding melt-growth process. Very well-textured single domain bulks of SmBCO with 5 wt% Ag 2O addition can be fabricated reproducibly under ambient atmosphere. Microstructure analysis of the obtained SmBCO/Ag bulk sample reveals that no silver particle is trapped within the mono-domain region, where the peritectic decomposition temperature goes back to the one of the Ag-free SmBCO sample. This c-axis oriented mono-domain region can be easily separated into a large amount of Sm123 seeds. Therefore, a new approach to preparation of Sm123 seed crystals in high quantity and quality can be achieved in an uncomplicated way, which exhibits significant advantage in comparison with the conventional method for Sm123 seed fabrication by MgO cold-seeding process. Experimental results show that a batch of well-textured YBCO bulks has been grown successfully by using these new Sm123 seed crystals.

Phase diagram of the La–Si binary system under high pressure and the structures of superconducting LaSi 5 and LaSi 10

The La–Si binary phase diagram under a high pressure of 13.5 GPa was experimentally constructed. New superconducting silicides LaSi 5 and LaSi 10 were found, which have peritectic decomposition temperatures at 1000 and 750 °C, respectively. The single crystal X-ray structural analysis revealed that there are two polymorphs in LaSi 5. The α-form obtained by heating a molar mixture of LaSi 2 and 3 Si at about 700 °C or by a rapid cooling from 1000 °C under pressure crystallizes with the space group C2 /m and the lattice parameters a=15.11(3), b=4.032(6), c=8.26(1) Å, and β=109.11(1)°. The β-form obtained by a slow cooling from 800–950 °C to 600 °C under pressure has the same space group but with slightly different lattice parameters, a=14.922(7), b=3.906(2), c=8.807(4) Å, and β=107.19(1)°. The β-form is formed during the incomplete transformation of the α-form on cooling, and has always been obtained as a mixture with the α-form. The compound can be characterized as a Zintl phase with a polyanionic framework ∞ 3 [ Si 5 ] 3 - with large tunnels running along the b axis hosting lanthanum ions. In the β-form, three of the five Si sites are disordered. The two polymorphs contain one dimensional sila-polyacene ribbons, Si ladder polymer, running along the b axis. The α-form showed superconductivity with the transition temperature T c of 11.5 K. LaSi 10 crystallizes with the space group 6 3/ mmc and the lattice parameters a=9.623(4), c=4.723(3) Å. It is composed of La containing Si 18 polyhedra (La@Si 18) of hexagonal beer-barrel shape, which form straight columns by stacking along the c-axis via face sharing. One-dimensional columns of La@Si 18 barrels are edge-shared, and bundled with infinite Si trigonal bipyramid chains via corner sharing. The Si atoms in the straight chains have a five-fold coordination. LaSi 10 became a superconductor with T c =6.7 K. The ab initio calculation of the electric band structures showed that α-LaSi 5 and LaSi 10 are metallic, and the conduction electrons mainly come from Si-3 p orbitals.

First-Principles Calculations and Thermodynamic Modeling of the Al2O3-Nd2O3System

Using first-principles calculations, the enthalpies of formation of NdAlO3 and Nd4Al2O9 from neodymia and alumina are predicted to be −41.1 and −104.5 kJ/mol-form, respectively, and Nd4Al2O9 is predicted to be a stable compound at all temperatures up to its peritectic decomposition temperature. In the case of NdAlO3, where reported experimental enthalpies of formation differ, our predicted value is used to determine which experimental value is more accurate. The enthalpies of formation calculated by the first-principles method are combined with experimental phase equilibria to evaluate the Gibbs energies of phases in the Al2O3–Nd2O3 system. The resulting Gibbs energy functions are compared with previous modelings of the system and are shown to be an improvement as more thermochemical data have been included. The combined first-principles/thermodynamic modeling approach employed in the current work shows promise in enabling the evaluation of important ceramic systems in which experimental thermochemical data are scarce.

The Effects of BaF&lt;sub&gt;2&lt;/sub&gt; Addition on Melt-Processed YBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7-x&lt;/sub&gt; Superconductors

The effects of BaF2 on thermal behavior and microstructure of melt-processed YBCO superconductors have been investigated. The differential thermal analysis (DTA) results indicated that the peritectic decomposition temperature of YBCO precursor powder was lowered when BaF2 was added (from 1020 to 976). The peritectic decomposition temperature was lowest at the content of 5 wt.% BaF2, and the variation of melting temperature was not significant above 5 wt.% BaF2. The microstructures of the doped samples have been observed by scanning electron microscopy (SEM). The results showed that the of BaF2 microstructure .

The effect of BaZrO 3 addition on melt-processed YBa 2Cu 3O 7– x superconductors

The effects of BaZrO 3 addition on the thermal behavior and microstructure of YBCO superconductors have been investigated. The differential thermal analysis indicates that the peritectic decomposition temperature of YBCO precursor powder is not change when BaZrO 3 is doped. The solidification temperature of YBCO changes with increasing of BaZrO 3 addition, thus the window of solidification temperature is affected. The results of scanning electron microscopy show that the BaZrO 3 particles are accumulated along the growth boundary, which result in the constitutional segregation of YBCO. The pushing–trapping theory is used to explain the phenomenon of segregation in the YBCO matrix.

Large multiseeded domains of (Y, RE)BaCuO obtained by the MUSLE technique

The multiseeded seamless bulk technique (MUSLE) developed by Sawamura et al for Dy/Gd/Ho-BaCuO compositions have been adapted for Y-based superconductors. This method allows overcoming the major problem encountered with the multiseeding technique, which is the trapping of non superconducting phases between the different domains. The MUSLE process requires the choice of two compositions for the bi-layer system. The criterion is a sufficient difference in the peritectic decomposition temperatures. In this condition, the higher peritectic temperature layer serves as nucleating site for the final YRE123 domain. Differential thermal analyses have been performed to select suitable compositions of as the upper layer and YYb123 as the lower layer. The influence of (Y, RE)2BaCuO5 (YRE211) composition on the crystal growth rate and on the superconducting properties was also investigated. Finally, compositions and thermal cycle have been defined to texture 2 cm multiseeded bi-layers samples. Electrical properties, coupled with SEM observations reveal the sample quality.

Gd–Ba–Cu–O bulk superconductors fabricated by a seeded infiltration growth techniqueunder reduced oxygen partial pressure

Single-grain Gd–Ba–Cu–O (GdBCO) bulk superconductors have beengrown by a seeded infiltration and growth (SIG) technique under a 1%O2+N2 atmosphere using a generic MgO-doped Nd–Ba–Cu–O (MgO–NdBCO) seed placed on thesample surface at room temperature (the so-called the cold-seeding method). Partial melting ofthe MgO–NdBCO seeds fabricated in air under notionally identical thermal processingconditions, however, limited the reliability of this bulk GdBCO single-grain process. Theobserved seed decomposition is attributed to the dependence of the peritectic temperatureTp ofMgO-doped Nd1+xBa2−xCu3Oy solid solution (MgO-doped Nd-123ss, where ss indicates solid solution) compounds on bothoxygen partial pressure during the melt process and the level of solid solution(x). The peritectic decomposition temperature of MgO-doped Nd-123ss, withx ranging from 0 to 0.5under p(O2) = 1.00 atm, was observedto remain constant at 1120 °C. Tp was observed to decrease linearly as a function of solid solutionlevel, on the other hand, under oxygen partial pressures of bothp(O2) = 0.21 and 0.01 atm. Based on these results, MgO-doped NdBCO seed crystals should be grownunder reduced oxygen partial pressure in order to obtain a stable MgO-doped NdBCO seedcrystal suitable for cold-seeding processes of large-grain (RE)BCO bulk superconductors(where RE is a rare earth element).

Influence of precursor calcination parameters on the critical current density of Bi-2212 superconductors

Partial melt-processed Bi 2Sr 2Ca 1Cu 2O 8+ δ (Bi-2212) materials have low critical current densities ( j c) when made from precursors where melting occurred during the calcination. In this paper, the origin of melt formation during calcination of a stoichiometric Bi:2, Sr:2, Ca:1, Cu:2 mixture of oxides and carbonates was identified and the consequences of this melt on the homogeneity of the calcination product and of fully processed Bi-2212 material studied. It was found that low oxygen partial pressure ( pO 2) atmospheres can build up inside the precursor particle network during the decomposition of the carbonates. This causes melt formation below 750 °C during calcination leading to phase separation and inhomogeneities in the calcined powder. The consequences of these inhomogeneities in the precursor on the j c of fully processed material and their microstructures was studied. In order to prevent melting below the peritectic decomposition temperature in the green bodies, the calcined precursors should be carbonate free but not yet fully converted to Bi-2212 in order to obtain maximum j c in partial melt-processed material. A calcined precursor that yields components of high j c shows maximal homogeneity on short length scales (<10 μm) just before it peritectically decomposes.

Influencia de la deficiencia de itrio en la sinterización de cerámicos YBaCuO (123)

En este trabajo se analiza la densificación del cerámico superconductor YBa2Cu3O7-x (123) a partir de compactos conformados con dos composiciones deficientes en itrio con respecto a la relación catiónica superconductora Y:Ba:Cu = 1,0:2,0:3,0. La evolución térmica de los polvos se estudió por ATD-TG, en atmósfera de O2, hasta la zona de descomposición peritéctica del sistema YBa2Cu3O7-x (» 1050ºC). La densificación de estos compactos se analizó por medio de dilatometrías realizadas bajo similares condiciones a las establecidas para los ATD-TG. Los mecanismos dominantes del sinterizado fueron analizados por medio de modelos aplicados a las curvas dilatométricas. De acuerdo a los datos combinados de dilatometrías y ATD-TG, se verifica que el mecanismo de sinterización por fase líquida (SFL) controla el 85% de la contracción total del compacto de composición Y0,7Ba2,0Cu3,3Ox (C2), el cual presenta un temprano crecimiento de granos (CG) desde los 860ºC. El proceso de CG no se detecta en el compacto de composición Y0,7Ba2,3Cu3,1Ox (C1) a temperaturas menores a los 900ºC. Para ambas composiciones se postula que, a partir de 900ºC, el mecanismo de SFL está presente por medio del proceso de reacomodamiento y luego, en el rango 930-975ºC, el mecanismo de solución-precipitación es el proceso dominante en el SFL.

Experimental study and thermodynamic re-assessment of the Al–B system

Controversial thermodynamic data in previous assessments of the Al–B system were used to identify a key experiment regarding the enthalpy of formation of AlB2 and its peritectic decomposition temperature. Experiments were performed using AlB2 powder purified by vacuum sublimation. Differential scanning calorimetry (DSC) in a heat-flux twin cylindrical Calvet-type calorimetric system was utilized to measure the enthalpy of decomposition and the reaction temperatures. Samples were characterized by X-ray powder diffraction (XRD). Based on that, a comprehensive and consistent re-assessment of the Al–B system was performed.The incongruent melting of AlB2 occurs at 972°C and a eutectoid decomposition of AlB2 at 213°C is predicted from the thermodynamic description. The present enthalpy data are supported by realistic values of absolute entropies of solid Al–B phases. The formation of AlB2 was never observed on cooling, it is extremely sluggish. Upon heating AlB2, the peritectic reaction does not produce perfectly crystalline AlB12. Based on that and constraints in the thermodynamic data, it is derived that the stability range of AlB2 in equilibrium with perfect crystalline AlB12 may be even more narrow than 972–213°C.

Study of&amp;lt;tex&amp;gt;$rm CeO_2+rm SnO_2+rm Ag$&amp;lt;/tex&amp;gt;Doped YBCO as a Candidate for Welding Composition

The doping mixture CeO/sub 2/+SnO/sub 2/+Ag has been added to YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(Y123). The basic idea was to combine the greatly enhanced superconducting properties of CeO/sub 2/+SnO/sub 2/ doped Y123 and the silver faculty to decrease the melting peritectic decomposition temperature of Y123, in order to use this material as a welding material for CeO/sub 2/+SnO/sub 2/ doped Y123 textured blocks. Consequently, different physico-chemical properties of this composition have been studied. It is shown that silver decreases the decomposition temperature of CeO/sub 2/+SnO/sub 2/ doped Y123 from at least 30/spl deg/C and that, for an addition of 5 wt%Ag, the critical current densities under all magnetic fields are totally similar to the CeO/sub 2/+SnO/sub 2/ doped Y123 ones. Hence, this composition appears really promising as a candidate for realizing high quality welds of CeO/sub 2/+SnO/sub 2/ doped Y123 blocks.