Experimental constraints on the phase diagram of elemental zirconium

The phase diagram of zirconium metal has been studied using synchrotron X-ray diffraction and time-of-flight neutron scattering at temperatures and pressures up to 1273 K and 17 GPa. The equilibrium phase boundary of the α-ω transition has a dT/dP slope of 473 K/GPa, and the extrapolated transition pressure at ambient temperature is located at 3.4 GPa. For the ω-β transition, the phase boundary has a negative dT/dP slope of 15.5 K/GPa between 6.4 and 15.3 GPa, which is substantially smaller than a previously reported value of −39±5 K/GPa in the pressure range of 32-35 GPa. This difference indicates a significant curvature of the phase boundary between 15.3 and 35 GPa. The α-ω-β triple point was estimated to be at 4.9 GPa and 953 K, which is comparable to previous results obtained from a differential thermal analysis. Except for the three known crystalline forms, the β phase of zirconium metal was found to possess an extraordinary glass forming ability at pressures between 6.4 and 8.6 GPa. This transformation leads to a limited stability field for the β phase in the pressure range of 6-16 GPa and to complications of high-temperature portion of phase diagram for zirconium metal.     

On the magnetic phase diagram of copper metaborate

A stepwise transition from one incommensurate state of the spin system of a copper metaborate crystal to another incommensurate state was previously revealed using neutron scattering in an applied magnetic field. In this paper, the new state is interpreted as a combination of a commensurate state of one spin subsystem and an incommensurate state of another spin subsystem of the crystal.     

Thermopower and phase diagram for pure solid and liquid samarium

Measurements of thermopower, S, for pure solid and liquid samarium are reported. Trends in S and dS/dT for the liquid light lanthanide metals are discussed. Based on these thermopower results and other work, a proposed phase diagram for Sm is presented.     

Martensite transformations and phase diagram of solid methane

Processing of the data of x-ray investigation of the diffraction scattering function of the 311 reflection in the temperature range 6–30°K shows that the phase transformation in methane is of the martensite type. The martensite points M_s and M_f limiting the region of the heterophase are determined on the phase diagram. The 16-molecule bct cell established in the-phase of CD₄ as well as the manifestation of birefringence in CH₄ and its isotopes leads to the conclusion that in these substances, as a result of molecular ordering, a lattice rearrangement from fcc to bct takes place, in accordance with the Bain orientation. The existence of an intermediate phase which is unstable in methane but stable in all its isotopes explains the presence respectively of one and two -anomalies in the specific heat.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 58–64, March, 1984.The authors are grateful to L. V. Skibina and M. M. Chernik for discussion of the results, and V. B. Filatova for assistance in the design of this experiment.     

Sound propagation anomalies and phase diagram of chromium alloys

Calculations of the complex elastic moduli Ĉ(T) in dilute Cr alloys are compared to measurements of the velocity and damping of sound near T _N and at high temperatures T>T _N (T _N — Néel temperature). The thermodynamic calculation is based on the covalent bond model of 3d ions in a state with different numbers n of covalent electrons. The parameters A _ij ⁽ⁿ⁾ of indirect exchange between the ions of the i and j sublattices are expressed in terms of the covalent bond energy Γ _ij ⁽ⁿ⁾ . The stability of the charge and spin density waves (CDWs and SDWs) is found by a variational method and is determined by the dispersion of Γ _ij ⁽ⁿ⁾ and by the Coulomb parameters U _n. For a small structural vector Q the phase diagram contains a superantiferromagnetic phase (SAFM) at temperatures T _N<T≲2T _N. The peak of the defect |ΔE(T)| of the modulus and of the sound damping Δ_h(T _N) near the first-order SDW-SAFM transition is determined by the structure of the transitional domain. Measurements of the anomalous growth of E(T) at temperatures T>T _N make it possible to determine the magnetostriction constants λ(T) of Ce alloys in the SAFM phase on the basis of the SAFM theory. Fiz. Tverd. Tela (St. Petersburg) 41, 1467–1472 (August 1999)     

Magnetic phase diagram of very dilute Pd-based alloys

The magnetic phase diagram of Pd-based 3d metal alloys is calculated on the basis of the random molecular field model. A paramagnetic-spin glass transition is expected for c < 0.06 at %, a paramagnetic-ferromagnetic one for c > 0.17 at %, while in the intermediate region a paramagnetic-ferromagnetic-spin glass transition is predicted.     

Unusual glass-forming ability of bulk amorphous alloys based on ordinary metal copper

We report the unusual glass-forming ability (GFA) of a family of Cu-based alloys, Cu46Zr47-xAl7Yx (0相似文献   

Theoretical justification of the magnetic phase diagram of CuMn alloys

Some important observations on the magnetic susceptibility of concentration Cumn alloys by Gibbs et al. are reinterpreted in the light of the mean-field theory of classical vector spin models with competing exchange interactions. The phase diagram proposed by Gibbs et al. is shown to be in qualitative agreement with the corresponding phase diagram predicted by mean-field theory.     

Positron trapping in the liquid and solid copper alloys

The peak counting rates of γ?γ angular correlation curves of positron annihilation (PCAC) in the liquid state fitted well to the straight line which had the same slope of the temperature dependence of the PCAC's attributed to the free annihilation in the solid state, for the Cu-8Ge and Cu-10.5Ge alloys and other copper solid solutions. The results of the positron trapping model fitting suggest the possibility that the positron in the liquid state repels the surrounding ions.     

A study of the Al-Cu-Co phase diagram and the solidification of alloys containing decagonal phase

The ternary Al-Cu-Co phase diagram was studied in order to revise the region of 50–75 at.% Al. The study was carried out by optical microscopy, scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Isothermal 800°C, 600°C and 540°C sections are presented. The development of the composition range of the decagonal phase with temperature is discussed.     

Possible link of the V-shaped phase diagram to the glass-forming ability and fragility in a water-salt mixture

Water is a very poor glass former, but its link to the thermodynamic and kinetic anomalies remains elusive. We experimentally reveal that the glass-forming ability and fragility of a water-salt mixture are closely related to its equilibrium phase diagram. We propose that frustration between local and global orderings controls both the glass-forming ability and the fragility. Relying on the same role of salt and pressure, which commonly break tetrahedral order, we apply this idea to pure water under pressure. This scenario not only explains unusual behavior of water-type liquids such as water, Si, and Ge but also provides a mechanism for a link between the equilibrium phase diagram, glass-forming ability, and fragility for various materials including oxides, chalcogenides, and metallic glasses.     

Hyperfine interaction and phase transitions in oxide films of zirconium alloys

Trimetallic Pt/Al₂O₃SnIn–Cl naphtha-reforming catalysts were prepared via co-precipitation route. Platinum and chlorine were introduced by the incipient wetness technique on the alumina support already doped with about 0.3 %wt of Sn to obtain about 0.3 %wt of Pt and 1.5 %wt of Cl. For the same Pt, Sn and Cl composition, indium loading ranged from 0.06 to 0.6 wt.%. The obtained catalysts were investigated by ¹¹⁹Sn Mössbauer spectroscopy between 95 and 300 K. Two Sn(IV), Sn(II) and Sn(0) environments have been identified and well characterized by their hyperfine parameters. The Lamb-Mössbauer factors have been determined for each environment and found to be 0.53, 0.27 and 0.31 for Sn(IV), Sn(II) and Sn(0) respectively. The addition of indium has been found to favour the formation of Pt_xSn alloys. ¹¹⁹Sn Mössbauer spectroscopy results show that addition of even small amount of In (0.06 wt.%) leads to the formation of a Pt₃Sn alloy. At higher indium loadings, higher amounts of Pt_xSn alloys of almost equal Pt and Sn atomic concentrations were detected. The increasing formation of Pt_xSn alloys with higher indium loading is in good correlation with a decrease of catalyst’s overall conversion and selectivity to C1 and C3–C4 paraffins and increase of isomerization selectivity.     

The phase diagram of the superconducting state of superconductor-band-antiferromagnet superlattices

The formation of the superconducting phase in short-period proximity-effect layered superlattices of the superconductor-band-antiferromagnetic-metal (SC/AF) type is studied. The exact solution of the Usadel equations is used to discuss the possibility of formation in such structures of a ground state in which the order parameters of the adjacent superconducting layers have opposite signs (the “π-phase”). The dependence of the superconducting transition temperature and the upper critical field normal to the layers on the lattice period, the intensity of magnetic interaction in the antiferromagnetic layer, and the state of the interface between the layers is examined. It is found that there exists a nonlinear dependence of the conditions for the appearance of the superconducting state in a layered SC/AF system on the system’s parameters. Finally, the conditions for the appearance of the superconducting phase in proximity-effect superlattices consisting of a superconductor with nonmagnetic, ferromagnetic, and antiferromagnetic metals are compared. Zh. éksp. Teor. Fiz. 111, 547–561 (February 1997)     

Ground state phase diagram of extended attractive Hubbard model

The ground state phase diagram of the weakly coupled extended Hubbard model with intraatomic attraction has been derived with the Hartree theory formulated in terms of the Bogoliubov variational approach. For a given value of electron density, the nature of the ordered ground state depends essentially on the sign and the strength of the nearest neighbor coupling. Some features are similar to those in the strong coupling limit obtained earlier.