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The isothermal sections of the Nd–Mg–Co phase diagram at 300 and 500 °C have been constructed on the basis of X-ray diffraction (XRD), Wavelength Dispersive Spectrometry (WDS) and Electron Probe Micro Analyzer (EPMA) analysis. The existence of two ternary compounds Nd 4 Mg 3 Co 2 (own structure type) and Nd 4 MgCo (Gd 4 RhIn type) was confirmed. The latter has homogeneity range defined as Nd 4- x Mg 1+ x Co with 0 ≤ x ≤ 0.2 at 300 °С and 0 ≤ x ≤ 0.3 at 500 °С. Four new ternary compounds were identified in this work: Nd 23- x Mg 4+ x Co 7 (Pr 23 Mg 4 Ir 7 type; −1.5 ≤ x ≤ 0.1 at 300 °С and −0.6 ≤ x ≤ 0.3 at 500 °С); NdMg 2 Co 9 (YIn 2 Ni 9 type), ∼Nd 77 Mg 14 Co 9 (cubic) and ∼Nd 56 Mg 6 Co 38 (unknown crystal structure). Two binary compounds, NdCo 2 and NdCo 3 , were found to dissolve significant amount of Mg with the formation of substitutional solid solutions Nd 1- x Mg x Co 2 (MgCu 2 type; x ≤ 0.1 at 300 °С and x ≤ 0.15 at 500 °C) and Nd 1- x Mg x Co 3 (PuNi 3 type; x ≤ 0.33 at 300 °С and x ≤ 0.5 at 500 °C), respectively. The Nd 4 Mg 3 Co 2 , Nd 4- x Mg 1+ x Co, Nd 23- x Mg 4+ x Co 7 and Nd 1- x Mg x Co 2 compounds irreversibly absorb hydrogen at room temperature and pressure 1–10 bar to form crystalline or amorphous hydrides with hydrogen content 1.6–2.1 wt. %. Hydrogen thermal desorption from these hydrides in vacuum results in their disproportionation with formation of binary NdH 2 hydride. The Nd 1- x Mg x Co 3 (0 ≤ x ≤ 0.5) alloys reversibly absorb up to 1.3 wt. % of hydrogen. NdMg 2 Co 9 compound has small hydrogenation capacity, absorbing only 0.5 wt. % at room temperature and hydrogen pressure 185 bar.

The isothermal section of the Tb–Mg–Co phase diagram at 500 °C has been built on the basis of XRD analysis of forty samples prepared by powder metallurgy. The existence of two ternary compounds Tb4Mg3Co2 and Tb4MgCo was confirmed. The formation of two solid solutions, Tb1−xMgxCo3 (0≤x≤0.4) and Tb1-−xMgxCo2 (0≤x≤0.6), was found for the first time. It is shown that Tb5Mg24 also dissolves a small amount of Co. Other binary compounds do not dissolve the third component. The Tb4MgCo and TbMgCo4 compounds form hydrides (12.7 and 5.3 at.H/f.u. capacity, respectively) that retain the original structure of metallic matrices. Upon thermal desorption the Tb4MgCoH12.7 hydride was stable up to 300 °C and disproportionated at higher temperature. Two other hydrides, Tb4Mg3Co2H∼4 and Tb2MgCo9H12, are unstable in air and decompose into the initial compounds.

The limited solid solution CeCu6−xZnx, x=0÷0.84 (structure type CeCu6, space group Pnma, Pearson code oP28, a=0.8112(1)÷0.8154(2), b=0.5102(1)÷0.5056(1), c=1.0162(2)÷1.0185(2) nm) was observed in the Ce–Cu–Zn ternary system at 200 °C. The homogeneity range of the solid solution was investigated by X-ray powder diffraction, wavelength dispersive spectrometry (WDS) and electron probe microanalysis (EPMA). X-ray single crystal diffraction was used for the detailed refinement of the crystal structure of CeCu5.16Zn0.84.

The crystal structure of new RTZn 2 intermetallic compounds (R = La, Ce, Tb; T = Co, Cu) was determined. The X-ray diffraction data showed that these compounds are isostructural to the new ternary compound ErCuCd 2 , which was found to crystallize with a superstructure of the ErCd 3 structure type (space group Cmcm, Pearson code oS16, a = 0.7097(1) nm, b = 1.0659(3) nm, c = 0.4471(1) nm, V = 0.3382(2) nm 3 , Z = 4). The obtained reliability factors are R F = 0.0240 and R W = 0.1127 for 235 unique reflections (|F 0 | > 4.00σ|F 0 |).

A new ternary compound LaCo 2.17 Zn 0.83 has been found during X-ray analysis of alloys in the La–Co–Zn system at 470 K. Single crystal measurements showed that this compound crystallised in the orthorhombic PrCo 2 Ga structure type (space group Pmma ). The refined structure parameters are a =5.038(1) A, b =4.047(1) A, c =7.124(2) A, V =145.3(1) A 3 , Z =8. The obtained reliability factor is R F =0.0316 for 292 independent reflections (| F 0 |>2 σ | F |).

The existence of the new ternary compound Tb 2 Co 2 Zn 15 has been found during an X-ray analysis of alloys in the Tb–Co–Zn system at 470 K. Single crystal measurements showed that this compound crystallised in the Ce 2 Al 2 Co 15 structure type (space group R3m ). The refined structure parameters are a =0.8984(5) nm, c =1.3150(4) nm, V =0.919(1) nm 3 , Z =3. The obtained reliability factor is R F =0.0494 for 245 independent reflections (| F o |>4.00 σ | F |).