Crystal structures, phase relationships, and magnetic phase transitions of R_5M_4 compounds (R = rare earths, M = Si, Ge)

Our recent studies of the crystal structures, phase transitions, and magnetic properties of intermetallic compounds RsM4 （R = rare earths; M = Si, Ge） are reviewed briefly. First, crystal structures, phase relationships, and magnetic prop- erties of several 5：4 compounds, including Nd5 Si4-xGex, Pr5 Si4_xGex, Gds-xLaxGe4, La5 Si4, and Gd5 Sn4, are presented. In particular, the canted spin structures as well as the magnetic phase transitions in PrsSi2Ge2 and PrsGe4 investigated by neutron powder diffractions and small-angle neutron scattering are reviewed. Second, the crystal structures and magnetic properties of the most studied compounds Gds（Si,Ge）4 are summarized. The focus is on the parent compound GdsGe4, which is an amazing material exhibiting magnetic anisotropy, angular dependent spin-flop transition, metastable magnetic response, Griffiths-like phase, thermal effect under pulsed fields, antiferromagnetic and ferromagnetic resonances, pro- nounced effects of impurities, and high-field induced magnetic transitions.

PHASE RELATIONSHIPS IN R-Fe PSEUDOBINARY SYSTEM (R=Dy_(0.65)Tb_(0.25)Pr_(0.1))

The phase relationships of R-Fe pseudobinary system(R=Dy0.65Tb0.25Pr0.1) have been determined using optical microscopy,X-ray diffraction,EPMA and DTA techniques.This system contains one eutectic reaction and four peritectic reactions.The four intermetallic compounds are(Dy,Tb,Pr)Fe2,(Dy,Tb,Pr)Fe3,(Dy,Tb,Pr)6Fe23 and(Dy,Tb,Pr) 2Fe17 The homogeneity regions of these compounds shift towards rare earth-rich side of the stoichiometric composition except(Dy, Tb,Pr) 2Fe17.

GRAPHICAL REPRESENTATION OF THE SUB-SOLIDUS PHASE RELATIONSHIPS IN THE RECIPROCAL SALT SYSTEM Si, Al, Y/N, O

This is a paper for the sub-solidus phase relationships in the full system Si_3N_4-A1NAl_2O_3-SiO_2-Y_2O_3-YN. Within this system there exist seventy-six compatibility tetrahedra.

PHASE RELATIONSHIPS IN QUASI-SYSTEMS R_2O_3-AlN-Al_2O_3(R=Ce,Pr,Nd,Sm)

The subsolidus phase relationships in the systems R_2O_3-AlN-Al_2O_3 (R=Ce, Pr, Nd.and Sm) and the isothermal section at 1700℃ of the Nd_2O_3-AlN-Al_2O_3 system have beendetermined. A nitrogen-containing R-β-alumina phase RAl_(12)O_(18)N has been identified. Theformation of the β-alumina phase occurring at both the compositions RAl_(12)O_(18)N and R_2O_3·11Al_2O_3 was explored in a series of light rare-earth systems. Single-phase N-containing β-aluminas can be obtained with the compositions RAl_(12)O_(18)N (R=La, Ce, Pr, Nd, Sm, andEu). However, La, Ce, Pr and Eu can also form β-alumina phase as the main phase at thecompositions of R_2O_3·11Al_2O_3, which form continuous solid solutions with RAl_(12)O_(18)N. Theunit cell dimensions of RAl_(12)O_(18)N have been determined to be α=5.557 (A) and c=22.00 (A) and there appears no deviation among the different R-β-aluminas (R=Ce→Sm)that can be detected. At 1700℃, an extensive liquid region exists in the triangle Nd_2O_3-Nd_2AlO_3N-NdAlO_3.

Phase Relationship in (Dy_(0.65)Tb_(0.25)Pr_(0.1))Fe_x Alloys (1.6≤x≤2.1)

The microstructure and phase relationship of (Dy0.65Tb0.25Pr0.1)Fex alloys in the composition range of 1.6≤x≤2.1 were investigated using optical microscopy, X-ray diffraction , DTA and EPMA techniques. The variations of microstructure and lattice parameter with the iron content,the effect of heat treatment on the microstructure and the phase relationship have been studied.The phase relationship in the vicinity of the Laves phase is proposed

Phase Relationship in Nd_2(Fe_(1-x)Ni_x)_(14) B and Pr_2(Co_(1-y)Ni_y)_(14)B Pseudo-ternary Compounds

The melting behavior,solid state phase transformation and structure of pseudo-ternary compounds Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B were studied using differential thermal analysis,optical microscopy X-ray diffraction,and electron probe micro-analysis techniques.At high temperature,eutectoid decomposition R_2(Ni,M)_(17)→R(Ni,M)_5+x-Ni(M) takes place in these two pseudo-ternary compounds,in the composition range x=0.6～1.0 and y=0.3～1.0,respectively.When x(or y)≤0.2,both Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B are single phase tetragonal.The phase constitutents of these two systems at room tempera- ture are similar in the composition range 0.6≤x(or y)≤1.0.

Phase equilibria of long-period stacking ordered phase in the ternary Mg-Y-Al alloys

Phase equilibria focusing on the long-period stacking ordered(LPSO)phases have been experimentally in-vestigated in the Mg-Y-Al alloys.The microstructures of the eleven representative alloys annealed at 450,500 and 550°C were systematically investigated using X-ray diffraction(XRD),scanning electron mi-croscopy(SEM)and transmission electron microscopy(TEM).Two thermodynamically stable LPSO poly-types were identified,including 18R and 10H structures.Meanwhile,the transformation of 18R→10H was detected in Mg-9.0Y-1.7Al(at.%)alloy,while the coexistence of 18R and 10H was observed in Mg-14.2Y-12.8Al(at.%)alloy.It was found that the LPSO phases were non-stoichiometric compounds with ternary solubilities.The 18R can dissolve up to 7.21 at.%-8.37 at.%Al and 10.75 at.%-12.01 at.%Y,while the 10H can dissolve up to 9.35 at.%-10.37 at.%Al and 14.50 at.%-14.94 at.%Y.All of the experimental re-sults were used to construct the isothermal sections,which is conducive to the design of Mg-Y-Al alloys.

Vertical sections of Tb_(0.15)Ho_(0.85)Fe_y-Tb_(0.3)Dy_(0.7)Fe_y(y=1.85, 1.9, 2.0) in Tb-Dy-Ho-Fe system

The x（Tb0.15Ho0.85Fey）＋（1–x）（Tb0.3Dy0.7Fey）（x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9; y=1.85, 1.9, 2.0） samples were prepared by a vacuum arc furnace, and annealed at 1000 oC for 1 d and at 950 oC for a week. Three vertical sections of Tb0.15Ho0.85Fey-Tb0.3Dy0.7Fey（y=1.85, 1.9, 2.0） in the Tb-Dy-Ho-Fe system were determined using optical microscopy, scanning electron microscopy, energy dispersion X-ray spectroscopy, X-ray diffraction, and differential thermal analysis. These vertical sections consisted of two single-phase regions： L and（Tb,Dy,Ho）Fe2; four two-phase regions： L＋（Tb,Dy,Ho）Fe3, L＋（Tb,Dy,Ho）Fe2,（Tb,Dy,Ho）Fe2＋（Tb,Dy,Ho）Fe3, and（Tb,Dy,Ho）Fe2＋（Tb,Dy,Ho）. The high Ho content of（Tb,Dy,Ho）Fey alloys led to the elevation of the peritectic temperature of L＋（Tb,Dy,Ho）Fe3→（Tb,Dy,Ho）Fe2. The region of（Tb,Dy,Ho）Fe2 phase was shifted towards the side of rich-Ho with the Fe content increasing. It meant that the substitution of Ho for Dy or Tb had a marked effect on the solidification process of（Tb,Dy,Ho）Fe2 compounds.