The decomposition and the re-formation of the (Bi, Pb)2Sr2Ca2Cu3O10+δ (Bi, Pb(2223)) phase have been investigated in situ by means of high-temperature neutron diffraction, both in sintered bulk samples and in Ag-sheathed monofilamentary tapes. Several decomposition experiments were performed at various temperatures and under various annealing atmospheres, under flowing gas as well as in sealed tubes, in order to study the appropriate conditions for Bi,Pb(2223) formation from the melt. The Bi,Pb(2223) phase was found to melt incongruently into (Ca, Sr)2CuO3, (Sr, Ca)14Cu24O41 and a Pb,Bi-rich liquid phase. Phase re-formation after melting was successfully obtained both in bulk samples and in Ag-sheathed tapes. The possibility of crystallizing the Bi,Pb(2223) phase from the melt was found to be extremely sensitive to the temperature and strongly dependent on the Pb losses. The study of the mass losses due to Pb evaporation was complemented by thermogravimetric analysis which proved that Pb losses are responsible for moving away from equilibrium and therefore hinder the re-formation of the Bi,Pb(2223) phase from the melt. Thanks to the full pattern profile refinement, a quantitative phase analysis was carried out as a function of time and temperature and the role of the secondary phases was investigated. Lattice distortions and/or transitions were found to occur at high temperature in Bi,Pb(2223), Bi,Pb(2212), (Ca, Sr)2CuO3 and (Sr, Ca)14Cu24O41, due to cation diffusion and stoichiometry changes. The results indicate that it is possible to form the Bi,Pb(2223) phase from a liquid close to equilibrium conditions, such as Bi(2212) and Bi(2201), and open new unexplored perspectives for high-quality Ag-sheathed Bi,Pb(2223) tape processing.

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.

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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.