Thermodynamic optimization of the Ho–Sn system

Фізика і хімія твердого тіла, 2019

The interaction of the components in the Ho−Cu−Sn ternary system was investigated at 670 K over the whole concentration range using X-ray diffraction and EPM analyses. Four ternary compounds were formed in the Ho-Cu-Sn system at 670 K: HoCuSn (LiGaGe type, space group P6 3 mc), Ho 3 Cu 4 Sn 4 (Gd 3 Cu 4 Ge 4-type, space group Immm), HoCu 5 Sn (CeCu 5 Au-type, space group Pnma), and Ho 1.9 Cu 9.2 Sn 2.8 (Dy 1.9 Cu 9.2 Sn 2.8-type, space group P6 3 /mmc). The formation of the interstitial solid solution based on HoSn 2 (ZrSi 2-type) binary compound up to 5 at. % Cu was found.

Journal of Alloys and Compounds, 2013

The phase diagram of the Ho-Te binary system has been assessed by using the CALPHAD (Calculation of Phase Diagrams) method on the basis of the experimental data of the phase equilibria and enthalpies of formation from ab initio electronic-structure calculations within the framework of density-functional theory. Reasonable models were constructed for all the phases of the system. The liquid phase was described as the substitutional solution model with excess energy expressed by Redlich-Kister polynomial. The compounds Ho 2 Te 5 and HoTe 3 were expressed as stoichiometric phases. The (HoTe) phase was modeled by two-sublattices; (Ho,Va) 1 (Te) 1. A consistent set of thermodynamic parameters has been derived, and calculated phase diagram was compared with the experimental data. A good agreement between the calculated results and experimental data was obtained.

Calphad, 2012

Based on experimental thermodynamic and phase equilibrium data, the Hf-Sn and Sn-Y systems have been modeled by computational thermodynamics using the CALPHAD method. The enthalpies of formation (D f H) for Hf 5 Sn 3 , Hf 5 Sn 4 and HfSn 2 (À 36.95, À 38.79 and À 27.96 kJ/mol-atom, respectively) obtained via first-principles calculations were used in the thermodynamic modeling. The solution phases including Liquid, (aHf), (bHf), (aY), and (bY) were modeled with the Redlich-Kister polynomial. The nine intermetallic compounds, i.e.

Chemistry of Metals and Alloys, 2016

The isothermal sections of the phase diagram of the Ho-Ag-Sn ternary system at 673 K and 873 K were constructed in the whole concentration range using X-ray diffraction and EPM analyses. The interaction between the elements results in the formation of three ternary compounds at 673 K: HoAgSn (LiGaGe-type, space group P6 3 mc, a = 0.4667(1), c = 0.7313(2) nm), Ho 3 Ag 4 Sn 4 (Gd 3 Cu 4 Ge 4-type, space group Immm, a = 0.4519(2), b = 0.7280(3), c = 1.5091(3) nm), and HoAgSn 2 (Cu 3 Au-type, space group Pm-3m, a = 0.4525(2) nm). At 873 K two ternary compounds (HoAgSn, LiGaGe-type and HoAgSn 2 , Cu 3 Au-type) were found. Three ternary compounds exist in the Tm-Ag-Sn system at 873 K: TmAgSn (ZrNiAl-type, space group P-62m, a = 0.72635(9), c = 0.4435(1) nm), Tm(Ag,Sn) 2 (CaIn 2-type, space group P6 3 /mmc, a = 0.46534(2), c = 0.72649(4) nm) and TmAgSn 2 (Cu 3 Au-type, space group Pm-3m, a = 0.45033(2) nm). DSC/DTA analyses showed a limited stability range for Ho 3 Ag 4 Sn 4 and the existence of a phase transition for the TmAgSn compound. DFT calculations predict metallic-like behavior for both HoAgSn 2 and Ho 3 Ag 4 Sn 4 .

Chemical Physics Letters, 1993

The heat of formation of HO2 has been determined using highly accurate ab initio calculations. Our computed value is 3.5 +0.5 kcal/mol at 0 K (or 2.8kO.5 kcal/mol at 298 K). The accuracy of the current result is estimated on the basis of calibration calculations on Hz, OH, H,O, 02, and H202, which are also discussed in this work.

Materials Science in Semiconductor Processing, 2014

We investigated the structural, elastic, and thermodynamic properties of HoX (X¼ N, O, S and Se), a series of pnictides and chalcogenides based on the rare-earth metal, Ho. These properties were studied by first-principles calculations of the total energy using the fullpotential linearized augmented plane wave method. Calculations were performed within the generalized gradient approximation for the exchange correlation potential. Structural parameters, namely, lattice parameter, bulk modulus and its pressure derivate, and cohesive energy with and without spin polarization of the structures NaCl, CsCl, ZB, tetragonal crystal, WC, NiAs, PbO, and wurtzite were determined. Elastic constants were derived from the stress-strain relation at 0 K. We also determined the thermodynamics properties for HoX through the quasiharmonic Debye model. The temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities, and Debye temperature at various pressures (0-50 GPa) and temperatures (0-1500 K) were predicted.

Physica B: Condensed Matter, 2006

The successive magnetic transitions and magnetic structure of hexagonal Ho 2 In compound have been investigated by the magnetic, specific heat and powder X-ray and neutron diffraction measurements. Two magnetic phase transitions have been observed at the paramagnetic to ferromagnetic transition temperature T c ¼ 85:0ð2Þ K and the magnetic order-order transition temperature T t ¼ 32:5ð2Þ K. No antiferromagnetic reflections have been observed in the neutron diffraction patterns. The Rietveld analysis has indicated that the Ho atoms possess different moment values at two inequivalent sites: 8.8(2) m B and 9.0(2) m B at 2 K and 7.0(2) m B and 7.4(2) m B at 45 K, respectively. The moment direction from the hexagonal c-axis is 41ð10Þ at 2 K. At 45 K, the reliability factor takes so shallow minimum at around 26ð20Þ that one cannot exclude the alignment of moments along the c-axis in the higher temperature phase. A model is suggested for the magnetic structure change at T t .

Thermochimica Acta, 2014

The compounds, Cr 2 TeO 6 (s), Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) were synthesized by solid-state route and characterized using X-ray diffraction technique. Thermal expansion of Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) were studied by high temperature X-ray diffraction technique in the temperature range 298-973 K and 298-923 K, respectively. The average volume thermal expansion coefficient of Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) were determined to be 2.46 × 10 −5 and 3.02 × 10 −5 K −1 , respectively. Heat capacity of Cr 2 TeO 6 (s), Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) was measured, in the temperature range of 300-870 K, employing temperature modulated differential scanning calorimeter. The Gibbs energy of formation of Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) were measured using transpiration method. An empirical function was derived to compute enthalpy of formation of A n TeO 6 (s) (where A = various elements of periodic table, n = 2, 3 or 6). Self consistent thermodynamic functions of Cr 2 TeO 6 (s), Fe 2 TeO 6 (s) and Ni 3 TeO 6 (s) were calculated. The chemical potential diagrams of ATe -O (A = Cr, Fe, Te) system were also constructed.

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