Quaternary intermetallics RE2Pt3Ga4In (RE=Y, Gd-Tm) – intergrowth structures of NdRh2Sn4 and TiNiSi related slabs

The quaternary gallium-rich intermetallic phases RE2Pt3Ga4In with RE = Y and Gd-Tm were synthesized by arc-melting of the elements and subsequent annealing. Small single crystals were obtained by high-frequency annealing of the samples in sealed tantalum ampoules. The polycrystalline samples were characterized through their X-ray powder patterns. The RE2Pt3Ga4In phases crystallize with a site ordering variant of the orthorhombic Y2Rh3Sn5 type, space group Cmc 21. The structures of Gd2Pt3Ga4In, Dy2Pt3Ga4.14In0.86, Er2Pt3Ga4.17In0.83 and Tm2Pt3Ga4.21In0.79 were refined from single-crystal X-ray diffraction data. The single crystals reveal small homogeneity ranges RE2Pt3Ga4±xIn1±x. The striking geometrical structural building units are slightly distorted trigonal prisms around the three crystallographically independent platinum atoms: Pt1@RE4Ga2, Pt2@RE2Ga4 and Pt3@RE2Ga2In2. Based on these prismatic building units, the RE2Pt3Ga4In structures can be described as intergrowth variants of TiNiSi and NdRh2Sn4 related structural slabs. Temperature dependent magnetic susceptibility studies of Gd2Pt3Ga4In and Tb2Pt3Ga4In show Curie-Weiss behavior and the experimental magnetic moments confirm stable trivalent gadolinium respectively terbium. Gd2Pt3Ga4In and Tb2Pt3Ga4In order antiferromagnetically at TN = 15.8(1) and 26.0(1) K. Magnetization curves at 3 K show field-induced spin reorientations.

Crystal Structure of the Compound Sc1.33Pd3Al8 with Layers of R Atoms and Al3 Triangles

The crystal structure of the new ternary aluminide Sc1.33Pd3Al8was refined by the Rietveld method from X-ray powder diffraction data. It crystallizes with a Gd1.33Pt3Al8-type structure:hR51-14.00,R-3m,a= 4.29142(4),c= 38.1638(4) Å,RB= 0.0344. The main feature of the structure is the statistical distribution of Sc atoms and Al3triangles within atomic layers of composition Sc2Al3(Sc0.67Al within the translation unit here), which is likely to correspond to stacking disorder of ordered layers. During the final cycles of the refinement, the occupancies of the corresponding sites were fixed at occ. = 2/3 for Sc in Wyckoff position 6cand occ. = 1/3 for Al in 18h. The unit cell of Sc1.33Pd3Al8contains six Sc0.67Al layers, nine Pd and eighteen Al atom layers along the crystallographic direction [001]. Together with the structure types Tb0.67PdAl3, Y2Co3Ga9, Sc0.67Fe2Si5, Er4Pt9Al24, Yb0.67Ni2Al6, and ErNi3Al9, the structure type Gd1.33Pt3Al8forms a family of intergrowth structures built up of three kinds of similar monoatomic layer.

Formation of metastable calcite-type barium carbonate during low-temperature decomposition of (Ba,Ti)-precursor complexes

(Ba,Ti)-precursor complexes, important for the production of advanced BaTiO3 perovskite-type materials, undergo structural transformations and complex reactions during their thermal decomposition. Based on XRD phase analysis, combined with Rietveld refinement of crystal structure data, and on IR analysis, the intermediate formation of calcite-type BaCO3 is evidenced, which can be explained by the stabilization of this metastable modification in the form of an oxycarbonate phase down to room temperature. Two possible processes, leading to such an oxycarbonate, are discussed: (i) partial substitution of CO32− by O2− in the anionic sublattice, and (ii) topotaxial formation of calcite-type structural domains of BaCO3 by templating with oxygen-deficient titanates, resulting in the oxide–carbonate intergrowth structures.

Rare earth-rhodium-plumbides RE2Rh2Pb with RE = La–Nd, Sm, Gd and Tb

The plumbides RE2Rh2Pb (RE = La–Nd, Sm, Gd, Tb) were synthesized in sealed niobium ampoules by induction melting of the pure elements or directly via arc-melting. The characterization of the samples by X-ray powder diffraction confirmed their Mo2B2Fe-type structure (space group P4/mbm) at room temperature. The Sm2Rh1.924Pb structure was refined from single-crystal X-ray diffractometer data: a=760.02(5), c=378.20(3) pm, wR=0.0387, 292 F2 values, 13 variables. The rhodium site shows small defects. The RE2Rh2Pb plumbides are simple 1:1 intergrowth structures of AlB2 and CsCl related slabs of compositions RERh2 and REPb. The Rh2 dumbbell in the SmRh2 slab of Sm2Rh2Pb shows a Rh–Rh distance of 281 pm. Temperature-dependent magnetic susceptibility measurements of La2Rh2Pb, Pr2Rh2Pb and Nd2Rh2Pb showed that the rhodium atoms carry no localized magnetic moments. La2Rh2Pb exhibits Pauli-paramagnetic behavior induced by the conduction electrons. The ground state of the praseodymium compound is ferromagnetic below TC=3.3 K while the neodymium compound shows a transition to an antiferromagnetic state at TN=6.1 K and a metamagnetic transition at a critical field of ca. 1000 Oe.

Superlattice-like structure and enhanced ferroelectric properties of intergrowth Aurivillius oxides

Aurivillius oxides with an intergrowth structures have been receiving increasing interest because of their special structures and potential outstanding ferroelectric properties.