The structure of the binary germanide Pr 4 Ge 7 has been determined by single-crystal X-ray diffraction on a twinned crystal. It is an ordered vacancy derivative of the α-ThSi 2 type, Pearson symbol oS44, space group C222 1 , a = 6.007(2), b = 13.987(4), c = 12.009(4) Å, isotypic to the structure reported earlier for Nd 4 Ge 7. The cell parameters of seven other praseodymium germanides observed in samples annealed at 873 K were refined from powder X-ray diffraction data.

Isothermal sections of the phase diagrams were constructed at 1073 and 773 K for the Pr-Ag-Si system and at 873 K for the Y-Ag-Si system based on X-ray powder diffraction data. The crystal structures of two ternary compounds in the Pr-Ag-Si system were refined by the Rietveld method: PrAg 2 Si 2 , СeAl 2 Ga 2-type structure, Pearson symbol tI10, space group I4/mmm, unit-cell parameters a = 0.42084(1), c = 1.06735(2) nm at 1073 K and CeNi 2+x Sb 2-x-type structure, oI10, Immm, a = 0.42088(2), b = 0.42287(2), c = 1.06695(3) nm at 773 K; PrAgSi, LiBaSi-type structure, hP3, P-6m2, a = 0.42302(1), c = 0.41911(1) nm at 1073 K and LaPtSi-type structure, tI12, I4 1 md, a = 0.42087(2), c = 1.46432(8) nm at 773 K.

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