M. Giovannini

The isothermal section at 500 °C of the Y-La-Mg ternary system

Ternary Y-La-Mg alloys have been studied by X-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. Phase equilibria have been established in the isothermal section at 500 °C in the 50 to 100 at. Pct Mg composition range. The sections (YxLa1-x) Mg (continuous solid solution), (YxLa1-xMg2 (cF24-Cu2Mg type for 0 ≤x ≤ 0.72 and hP12-MgZn2 type for 0.82 ≤x ≤ 1 solid solutions), and YxLa1-xMg3 (0 ≤x ≤ 0.47) have been especially studied. The ≈YxLa1-xMg5 (0.35 ≤x ≤ 0.77) ternary compound (cF440-GdMg5 type) has been found. A reinvestigation of selected regions of the binary La-Mg and Y-Mg systems proved necessary. The La5Mg41 phase, not previously reported, has been found by the annealing of samples at 600 °C. The YMg2 phase shows a wide homogeneity range up to 73 at. Pct Mg. The ternary section has been compared with a simulated one that was created by placing sections of binary systems of Mg with different rare earth elements side by side. The results are related to the pseudolanthanide concept.

Structural chemistry, magnetism and thermodynamic properties of R2Pd2In

We report on magnetisation, resistivity and specific heat measurements of R2Pd2In compounds synthesised with the nominal composition R40Pd41In19 (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y). Magnetic and thermodynamic measurements reveal antiferromagnetic order below 32 K for this series except for Y, La, Yb and Lu. An appreciably wide homogeneity range is found for Ce2Pd2+xIn1−x where ferro- or antiferromagnetic order or both occur with typical features of a Kondo lattice. Yb2Pd2In exhibits intermediate valent behaviour and no magnetic order could be detected down to 0.3 K.

Thermal conductivity of superconducting MgB2

Thermal conductivity of superconducting MgB2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below Tc was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.

The praseodymium-gold system

Abstract The phase diagram of the PrAu system was examined over the whole composition range by differential thermal analysis, X-ray diffraction, optical and scanning electron microscopy, and electron probe microanalysis. Seven intermetallic compounds form in the PrAu system. Their melting behaviour was determined and their crystal structures confirmed or determined as follows: (1) Pr 2 Au, orthorhombic, oP 12, Co 2 Si-type (anti-PbCl 2 -type), peritectic formation 750 °C: (2) PrAu. m.p. 1420°C (α form, orthorhombic, oP 12, FeB-type; β form, orthorhombic; o C8, CrB-type; γ form, cubic, c P2, peritectic decomposition 1250°C: (4) PrAu 2 , orthorhombic, ol 12, CeCu 2 -type, peritectoidal decomposition 110° C: (4) PrAu 2 tetragonal, tp 106, Nd 17 Au 16 -type m.p. 1180°C; (6) Pr 14 Au 41 , hexagonal, hP 65. Gd 14 Ag 51 -type, m.p. 1210°C; (7) PrAu 6 , monoclinic, mC 28, PrAu 6 -type peritectic decomposition 900°C. Four eutectic points exist at 610°C and 18.0 at.% Au 1100°C and 62.0 at.% Au, 1050°C and 72.5 at.% Au, and 790°C and 90.5 at.% Au. A catatectic reaction of the (βPr) phase was also found.

Isothermal section from 50 to 75 at.% Mg of the ternary system YLaMg

Abstract The ternary system YLaMg has been studied in the 50–75 at.% Mg composition range using microscopic and X-ray diffraction analyses. The sections (Y x La 1- x )Mg (continuous cP2-CsCl-type solid solution), (Y x La 1- x )Mg 2 (cF24-Cu 2 Mg-type solid solution for 0 ⩽ × ⩽ 0.72 and hP12-MgZn 2 -type solid solution for 0.82 ⩽ × ⩽ 1) and Y x La 1- x Mg 3 (0 ⩽ × ⩽ 0.47, cF16-BiF 3 -type solid solution) have been especially studied.

Characterization and physical properties of the indides Yb2T2In (T=Cu, Pd, Au)

Abstract The ternary compounds Yb2T2In (T=Cu, Pd and Au) have been synthesized. The indides Yb2Au2In and Yb2Pd2In crystallize in the Mo2FeB2 structure type, while Yb2Cu2In proved to be isotypic with the W2CoB2 structure. Magnetic, resistivity and specific heat measurements revealed no magnetic order for any of the compounds but, while in Yb2Cu2In and Yb2Au2In the valence of Yb was observed to be ν=2, Yb2Pd2In exhibits intermediate valence behavior.

Phase relationships at 500 °C in the YPrMg system

Abstract Phase equilibria in the ternary system YPrMg have been studied by X-ray powder diffraction analysis, optical and scanning electron microscopy, and electron probe microanalysis. The isothermal section at 500 °C has been determined in the range 50–100 at.% Mg. The phase equilibria are characterized by the formation of the following rather extended solid solutions: (Y x Pr 1− x )Mg (continuous solid solution of cP2-CsCl type) and Y x Pr 1− x Mg 3 (0 ⩽ x ⩽ 0.5) of cF16-BiF 3 type. A cubic phase of (Y x Pr 1− x )Mg 2 , (cF24-CuMg 2 type) derived from the binary PrMg 2 phase by a substitution of Pr with Y has been observed in a narrow range close to x ≈ 0.6. A solid solution based on the binary YMg 2 phase, i.e. ( Y x Pr 1− x )Mg 2 + y of hP12-MgZn 2 type (0.79 ⩽ x ⩽ 1, for y = 0), extends into the ternary field. The ternary compound Y x Pr 1 − x Mg 5 (0.3 ⩽ x ⩽ 0.9) of the cF440-GdMg 5 type has been established. Finally, the YPrMg section has been compared with the similar YLaMg section studied previously and with an isothermal section predicted on the basis of the systematic trends of the rare earth alloy properties.

The magnetic instability of Yb2Pd2(In,Sn) in a non-Fermi liquid environment

Various concentrations of the solid solution Yb 2 Pd 2 In 1-x Sn x ranging from x = 0 to 1 with the tetragonal Mo 2 FeB 2 -type structure were prepared and their physical properties were studied by means of bulk and spectroscopic measurements as a function of temperature, pressure and magnetic fields. Results deduced from these studies indicate a slight variation of the valency of the Yb ions, from v 2.9 for both border compounds to v = 3 at x = 0.6. This variation gives rise to the appearance of long range magnetic order in a narrow concentration region around x = 0.6, while both border compounds remain non-magnetic. The outstanding concentration dependence for the ordered regime may be indicative of two quantum critical points, a novel feature not yet observed in Yb compounds.

On the magnetic and valence properties of CeMgY compounds

The structural and magnetic properties of a series of novel compounds in the ternary CeMgY system have been studied by X-ray diffraction. SQUID magnetometry and XAS spectroscopy. The crystal structures of the compounds Ce0.34Y0.67Mg2 and Ce0.49Y0.51Mg4.7 have been refined by the Rietveld technique. Magnetic data are consistent with a tripositive ground state 2F52 for the cerium atom. The XAS measurements confirm this result. Crystal field effects are apparent in the magnetic data at temperatures below about 50 K in the compounds with higher Ce concentration.

The isothermal section at 450°C of the Yb–Pr–Mg system

Abstract In the framework of a systematic investigation of the ternary alloys formed by magnesium with two different metals of the rare earth family, data obtained in a study of the Yb–Pr–Mg system are presented. In the isothermal section at 450°C, phases have been identified which are based on the ternary extensions of the binary compounds PrMg, PrMg3, Pr5Mg41 and YbMg2. The PrMg12 compound on the contrary shows very small ternary solid solubility. Two ternary compounds have also been identified: τ1, (YbxPr1-x)Mg2 (0.15⩽x⩽0.48), cF24–MgCu2 Laves type and τ2,≈(YbxPr1-x)Mg4.5 (0.12⩽x⩽0.40), cF440–GdMg5 type. The trends of the lattice parameters and the general features of the isothermal section are discussed and compared with those of other magnesium ternary alloys with rare earth elements. The behaviour of the different MeMg2 Laves phases is particularly highlighted.