CALCULATION OF THE EXCHANGE INTERACTION CONSTANT BETWEEN RARE-EARTH AND TRANSITION METAL SUBLATTICESIN R_2Fe_(17_x)Al_x(R=Tb, Gd AND Dy)COMPOUNDS

An approximate calculation of the exchange interaction constant J_(RT)between the rare-earth sublattice and the transition metal sublattice in R_2Fe_(17-x)Al_x (R= Tb,Gd, and Dy) compounds is given by the molecular-field model and the results of neutron diffraction.The calculated values, -J_(R,T)/k, for Dy_2Fe_(17-x)Al_x (x=5, 6, 7 and 8), Tb_2Fe_(10)Al_7,Gd_2Fe_(17-x)Al_x (x=7, 8) compounds are 8.62K, 8.64K, 9.52K, 10.34K and 10.66K, 10.65K, and 9.85K,respectively, they are in agreement with the experimental values, -J_(R,T)/k, of Dy_2Fe_(17-x)Al_x(x=5, 6, 7 and 8), Tb_2Fe_(10)Al_7 and Gd_2Fe_(17-x)Al_x (x=7, 8) compounds, which are 8.77K, 9.25K,10.1K, 10.9K and 10.35K, 10.1K, and 10.3K, respectively. The origins of the difference between thecalculated and the experimental results are discussed.

Thermodynamic assessment of Au-Zr system

Au-Zr binary system was reassessed by using the calculation phase diagram （CALPHAD） technique based on experimental thermodynamic data and newly reported phase diagrams. The excess Gibbs energies of the three terminal solutions and the liquid phases were formulated with Redlich-Kister polynomial. All the intermetallic phases were treated as stoichiometric compounds with the exception of ZrAu which is modeled by a two-sublattice model, （Au,Zr）∶（Au,Zr）. The results show that there exist seven intermetallics: Zr3Au, Zr2Au, Zr5Au4, Zr7Au 10 , ZrAu2, ZrAu3, and ZrAu4 in the system. The eutectoid reaction: β （Zr） → α （Zr）+Zr3Au takes place at 1 048 K and the maximal solubility of Au in α -Zr is 4.7%（mole fraction）. The maximal solubility of Zr in Au is 6.0% （mole fraction） at 1 347 K. The homogeneity range of ZrAu phase is about 44.5%-52.9%（mole fraction） of Au. The present assessment fits experimental data very well.

Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

Modelling thermodynamics of nanocrystalline binary interstitial alloys

Grain boundary （GB） segregation in nanocrystalline alloys can cause reduction of GB energy, which leads to thermodynamic stabilization of nanostructures. This effect has been modelled intensively. However, the previous modelling works were limited to substitutional alloy systems. In this work, thermodynam- ics of nanocrystalline binary interstitial alloy systems was modelled based on a two-sublattice model proposed by Hillert [M. Hillert, et al. Acta Chem. Scand., 24 （1970） 3618] and an atomic configuration for nanocrystalline systems proposed by Trelewicz and Schuh LI.R. Trelewicz, et al. Physical Review B, 79 （2009） 094112]. The modelling calculations agree with the reported experimental data, indicating that the current thermodynamic model is capable of accounting for the alloying effect in the nanocrystalline binary interstitial alloys.

Experimental study and thermodynamic calculation of Lu2O3-SiO2 binary system

As a binary system of BaO-Lu_2O_3-SiO_2 ternary system, Lu_2O_3-SiO_2 system was optimized and calculated by CALPHAD approach based on available phase diagram and relevant thermodynamic data of RE_2O_3-SiO_2（RE=Lu,Yb,Y） binary systems as well as our experimental data of Lu_2O_3-SiO_2 system obtained by quenching experiment. The Gibbs free energy of high temperature solution was described by an ionic two-sublattice model as（Lu^（3＋））P（O^（2-）, SiO_2~0）Q. The calculated phase diagram below 1873 K was in good agreement with experimental data at 1573, 1773 and 1873 K. The calculated Gibbs energies of two intermediate phases Lu_2SiO_5 and Lu_2Si_2O_7, the activity of Lu_2O_3 and SiO_2 and specific heat capacities of intermediate phases agreed well with experimental results of Y_2O_3-SiO_2 system. This tentative study will offer help for the research of single-phase phosphor and related metallurgical slags, refractories, high-temperature superconductivity material systems.