Intermultiplet crystal field transitions in EuNiO3

We determined the energy splitting of the ⁷F₁ multiplet of Eu³⁺ in EuNiO₃ using inelastic neutron scattering. We were able to retrieve accurate values for the second order crystalline electric field parameters, which will allow a more reliable determination of the crystalline electric field potential in the RNiO₃ (R=rare earth) series. This is essential for a possible observation of a charge transfer, which is proposed by one of the models describing the observed metal-to-insulator transition in these compounds.     

Ultrasound studies of phase transitions in tungsten bronze ferroelectric materials

Attenuation and velocity measurements at ultrasonic frequencies were performed in two ferroelectric solid solutions with tungsten bronze structure type, SBN and PBN, as a function of temperature (from 200 to 380 K). Both materials, in polycrystalline form, presented sensitive changes in the temperature dependence curves of attenuation and velocity. One of these anomalies (at 350 K for SBN and 323 K for PBN) was associated with a second-order phase transition, confirming the ferroelectric orthorhombic–ferroelectric tetragonal phase transition suggested for both systems in this temperature range.     

Thermodynamic modeling of the CeO2–CoO phase diagram

A thermodynamic modeling of the CeO₂–CoO phase diagram was performed with recent experimental data. The excess Gibbs energies of the solution phases were described on the basis of the simple regular solution. A consistent set of optimized interaction parameters was derived for describing the Gibbs energy of each phase in this system leading to a good fit between calculation and experimental data. The liquidus, solidus, and solvus curves were calculated and also the lattice stabilities of the components were evaluated.     

A new type of FCT martensite phase in single-crystalline Fe3Pt Invar alloy

Martensitic transformation in a highly ordered Fe₃Pt has been investigated by magnetization and X-ray diffraction measurements. We confirmed that a new type of face-centered tetragonal (FCT) martensite phase appears below 60 K in Fe₃Pt with a degree of order S = 0.88. The tetragonality c/a gradually increases with decreasing temperature, and is approximately 1.005 at 10 K. This is in contrast to the tetragonality c/a < 1 generally observed in the FCT martensite with a degree of order less than 0.8. The spontaneous magnetization increases in association with the transformation.     

Magnetocaloric effect in the Ce2Fe17−xMnx helical magnets

The Ce₂Fe_17−xMn_x (x = 0-2) compounds demonstrate a complex temperature dependence of the magnetocaloric effect MCE, which is inverse in a narrow temperature interval just below Néel temperature T_N and normal at higher or lower temperatures. The normal MCE exhibits two peaks in the vicinity of temperatures of ferromagnetic ordering Θ_T and T_N for compositions x = 0-0.35, 1.3-2 or one peak near T_N for antiferromagnets with x = 0.5-1. The maximal change of the peak entropy −S_M is about 3 J/kg K in a field of 5 T for the compounds with x = 0-0.5 at T ∼230 K close to T_N. The drastic decrease of the MCE, by half, in the Ce₂Fe_17−xMn_x system is traceable to a decrease of the spontaneous magnetization and the helical type of magnetic states in the compounds.     

The high temperature phase transitions of orthorhombic La0.95MnO3

The high temperature phase transitions of orthorhombic La_0.95MnO₃ from room temperature to 1273 K were studied using high temperature XRD technique in air. Two-phase transitions were found in temperature ranges, 373–473 K and 973–1273 K, respectively. The crystal symmetry increases from orthorhombic to rhombohedral then cubic, while the second transition was not completed in the observation of the present study. The first transition could be due to the depression of Jahn–Teller distortion, while the second one could be caused by the ionic oscillation at high temperature. The lattice thermal expansion coefficients of rhombohedral La_0.95MnO₃ from 473 to 973 K were also calculated using lattice parameters.     

Electrochemical syntheses of soft and hard magnetic Fe50Pd50-based nanotubes and their magnetic characterization

Near-equiatomic Fe-Pd-based nanotubes with diameters of 200 nm and lengths of 1 μm were directly electrodeposited from a single electrolyte into polycarbonate templates. The as-deposited Fe₅₀Pd₅₀ nanotubes were then characterized compositionally, structurally and magnetically. The as-deposited Fe₅₀Pd₅₀ tubes had an fcc crystal structure and were magnetically soft (H_C ≈ 10 kA/m), with the easy axis of the magnetization being parallel to the axes of the tubes. Angular-dependence measurements of the coercivity, where the hysteresis loops were measured as a function of the angle (θ) of the applied demagnetizing field, revealed a combination of magnetization reversal mechanisms, consisting of the curling mechanism, which dominates at low angles, with a transition to coherent rotation at angles ≥70°. The development of the coercivity with annealing temperature due to the L1₀ ordering was also investigated. For this purpose the as-deposited nanotubes were annealed at temperatures from 400 °C to 650 °C for 1 h in Ar + 7% H₂ and the phase formation, the microstructure and the magnetic properties were analyzed. A maximum in the coercivity of 135 kA/m was achieved upon annealing at 550 °C.     

Experimental determination and thermodynamic assessment of the phase diagram in the Co–Zr system

The phase diagram in the Co–Zr system was determined using the electron probe microanalyzer (EPMA), differential thermal analysis (DTA) and X-ray diffraction (XRD) technique. The experimental results indicate that (1) the solubility region of the Co₂Zr phase is from 25 to 34 at.% Zr; (2) the CoZr₃ phase exists and the temperature of the peritectoid reaction (CoZr₂ + (βZr) ↔ CoZr₃) is about 981 °C; (3) the solubilities of Zr in the (αCo) phase and Co in the (βZr) phase are about 0.15 and 2.5 at.%, respectively. A thermodynamic assessment of the Co–Zr binary system was carried out by the CALPHAD (calculation of phase diagrams) method. The Gibbs free energies of the solution phases (liquid, fcc, bcc and hcp) were described by the subregular solution model, and those of the intermetallic compounds (Co₁₁Zr₂, Co₂₃Zr₆, Co₂Zr, CoZr, CoZr₂ and CoZr₃) were described by the sublattice model. A proper set of the thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Co–Zr system. An agreement between the calculated results and experimental data is obtained.     

Large magnetic entropy change near room temperature in La0.7(Ca0.27Ag0.03)MnO3 perovskite

In this paper, the magnetic properties and magnetocaloric effect (MCE) of La_0.7(Ca_1−xAg_x)_0.3MnO₃ (x = 0, 0.1, 0.2, 0.7, and 1) powder samples are reported. Our polycrystalline compounds were synthesized using the solid state reaction method at high temperature. Magnetization measurements versus temperature showed that all our samples exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature, T_C, has been found to increase from ∼250 K for x = 0-270 K for x = 1. Ag doping weakens the first order phase transition, and at higher Ag doping, the phase transition is of second order. For the La_0.7(Ca_0.27Ag_0.03)MnO₃ composition, the maxima of the magnetic entropy changes from the applied magnetic field (ΔS_M) at 2 and 5 T are about 4.5 and 7.75 J/kg K, respectively, at the Curie temperature of ∼263 K. The relative cooling power (RCP) values without hysteresis loss are about 102 and 271 J/kg for the applied fields of 2 and 5 T, respectively. Due to the large ΔS_M, large RCP, and high Curie temperature, La_0.7(Ca_0.27Ag_0.03)MnO₃ is promising for application in potential magnetic refrigeration near room temperature.     

Thermodynamic assessment of the Mo–Re binary system

The existing Mo–Re phase diagrams are reviewed and a thermodynamic calculation of the Mo–Re binary system is undertaken. The Gibbs energies are estimated for liquid, bcc (Mo), hcp (Re), σ and χ phases. The liquid, bcc (Mo) and hcp (Re) phases are described by a regular solution model, whereas the σ and χ phases are described respectively by three-sublattice models. For the σ phase, two thermodynamic models are used for calculations and the results are compared. The models take into account the crystallographic structure and similarity between the σ and χ phases. The calculated results remove the ambiguity of the existing phase diagram data and are compared with the experimental data in the literature.     

Thermodynamic modeling of the Ca–Ag binary system

The Ca–Ag binary system has been assessed with CALPHAD approach based on experiment information about phase diagram and thermodynamic properties. The excess Gibbs energies of the solution phases including liquid, bcc and fcc were formulated with Redlich–Kister polynomial functions. The intermetallic compounds Ca₂Ag₉, Ca₂Ag₇, CaAg₂, CaAg, Ca₅Ag₃ and Ca₃Ag were treated as stoichiometric phases. Self-consistent thermodynamic parameters have been obtained and the calculated results agree well with most literature data. Several diagrams and tables concerning the Ca–Ag system are presented.     

Role of strontium addition on the phase transition of lanthanum copper oxide from K2NiF4 to perovskite structure

Without Sr addition, the sintered La₂O₃ and CuO powder mixture in a mole ratio of 1:2 formed K₂NiF₄-structured La₂CuO₄ with excess CuO. When 15% of strontium was added, La₂CuO₄ transformed into the single perovskite La_1−xSr_xCuO_2.5−δ phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu²⁺) to trivalent ones (Cu³⁺) by the strontium addition. Based on the electroneutrality in an ABO₃ perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La³⁺. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu²⁺ ion into trivalent Cu³⁺ ion was enhanced. The increase of Cu³⁺ concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained.     

Evaluation of glass forming ability in ternary Ni62(Nb,Ta)38 alloys

The parameter γ¹ we previously defined has been proved to be valid in predicting the better glass former in several binary alloy systems, but is hard to be applied in the multi-component alloys because the phase diagrams of these alloys are usually not well constructed. In the present work, we attempt to extend the application of parameter γ¹ to a ternary alloy system and predict the better glass former in the Ni₆₂Nb_38-xTa_x (x = 5, 10, 15, 20, 25, 30, 35) alloys based on the systematic investigation on the phase evolution from Ni₆₂Nb₃₈ to Ni₆₂Ta₃₈. The prediction has been confirmed by the experimental results, indicating the validity of the parameter γ¹ in the Ni₆₂(Nb, Ta)₃₈ ternary alloys.     

Structural evolution during crystallization in phase separated Ti–Y–Al–Co metallic glass

Structural evolution during heat treatment of melt spun Ti₃₆Y₂₀Al₂₄Co₂₀ alloy was studied using differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. The as-melt spun Ti₃₆Y₂₀Al₂₄Co₂₀ specimen showed a hierarchical complex microstructure consisting of Ti-rich and Y-rich amorphous phases and crystallized with two-step process. Crystallization in the phase separated two phase mixture took place in a confined mode due to different thermal stability and complex microstructure, resulting in various nano-scaled microstructural formation ranging from fine distribution of crystalline particles in amorphous matrix to fine distribution of amorphous particles in crystalline matrix.     

First-principles investigation of phase stability,elastic and thermodynamic properties in L12 Co3(Al,Mo,Nb) phase

First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co₃(Al,Mo,Nb) with the L1₂ structure. Calculated elastic constants show that Co₃(Al,Mo,Nb) is mechanically stable and possesses intrinsic ductility. It is found that the shear and Young's moduli of Co₃(Al,Mo,Nb) are smaller than those of Co₃(Al,W). Calculated density of states indicate the existence of covalent-like bonding in Co₃(Al,Mo,Nb). Temperature-dependent thermodynamic properties of Co₃(Al,Mo,Nb) can be described satisfactorily using the Debye-Grüneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data can be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys.     

The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction

By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd_0.9Ni_0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites. We provide experimental evidence for the occurrence of an isostructural phase transition in TbPd_0.9Ni_0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd_0.9Ni_0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd_0.9Ni_0.1Al undergoes two successive magnetic phase transitions at T_N1=41 K and T_N2≈21.5 K. Two third of non-frustrated ordered Tb moments form commensurate antiferromagnetic chains () and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure () between T_N2 and T_N1 to an incommensurate structure () below T_N2. Due to the strong magneto-crystalline anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) μ_B (non-frustrated) and 7.2 (2) μ_B (frustrated). The symmetry of the magnetic structure of TbPd_0.9Ni_0.1Al is lower than that of TbNiAl.     

Phase transformations in the B2 phase of Co-rich Co-Al binary alloys

Phase transformations in the β (B2) phase of Co-21 and -23 at.% Al alloys were examined using transmission electron microscopy, energy dispersive X-ray spectroscopy and differential scanning calorimetry. The microstructures obtained from as-quenched specimens were found to be strongly affected by the quenching condition. While relatively thick sheet-specimens with a lower quenching rate showed bainitic plate precipitates with a fcc structure, a martensite-like structure was observed by optical microscopy in relatively thin specimens with a higher quenching rate. Regardless of the quenching condition, a spinodal-like microstructure composed of A2 and B2 phases was also detected and the A2 phase changed to a metastable hcp phase during further aging.     

Changes in the phase structure and magnetic characteristics of Gd5Si2Ge2 when alloyed with Mn

Gd₅Si₂Ge₂ parent compounds were alloyed with Mn in order to understand the underlying relation between the structural phases and the magnetic behavior of the pseudo ternary compounds formed. The alloying mechanism in Gd₅Si₂Ge₂ causes simultaneous substitution of the nonmagnetic Si and Ge atoms from the (Si + Ge) sublattice in equal amounts. No subsequent heat treatment was made on alloyed compounds. X-ray powder diffraction, magnetization versus temperature and isothermal magnetization measurements were carried out. X- ray diffraction patterns were used to qualitatively determine the existence of different structural phases in the alloys. It was observed that the starting, as-melted alloy with z = 0 has Gd₅Si₄-type orthorhombic structure at room temperature with traces of 1:1 stoichiometry phase which transforms totally to a Gd₅Si₂Ge₂-type monoclinic phase when heat treated. Similarly, increase in the Mn content leads to an increase in the monoclinic phase content of the originally orthorhombic compounds. Curie temperatures were determined from M(T) measurements and the magnetocaloric characterization was made using M(H) measurements by plotting the magnetic entropy change values against temperature. No giant magnetocaloric effect was observed for non heat treated samples.