Inmaculada Mas Álvarez

Structural characterization and semiconducting properties of new iridium(IV) perovskites

Abstract New perovskite-type compounds La 2 MlrO 6 (M = Mg, Co, Ni, Cu, Zn) have been synthesized by solid state reaction in air. They have been characterized from X-ray diffraction data by means of the Rietveld method. These materials show a monoclinic symmetry (S.G. P2 1 /n). Electron microscopy patterns are indexed as a result of the existence of multitwinning. Electronic conductivity measurements have been carried out, in the range 300–650 K, and a p-type semiconductor behaviour is observed. Activation energies are close to 0.2 eV in all cases. These results are of interest because there is a lack in the knowledge of iridium perovskites and in their properties, which is a contrast to the case of other 4d and 5d elements.

Magnetic characterization of the LaNi1−xSbxO3(0≤x≤13) perovskite-like system

Abstract The magnetic characterization of the LaNi1−xSbxO3 (0≤x≤ 1 3 ) perovskite-like system is reported. These compounds can be regarded as being derived from LaNiO3 by partial substitution of Ni3+ by Sb5+ cations with the concomitant partial reduction of Ni3+ to Ni2+. Formally, for x=0 only Ni3+ is present, whereas for x= 1 3 Ni cations are stabilized as Ni2+. Magnetic susceptibility measurements show that a transition from a Pauli paramagnetic behaviour (x=0.05) to complex magnetic interactions takes place in this system. The nature of such interactions is interpreted as antiferromagnetic with an important canting of the spin arrangement, giving rise to a noticeable ferromagnetic component. These results have been qualitatively confirmed using the EPR technique.

Structural characterization and magnetic susceptibility of Ba2RIrI6 distorted perovskites (R = rare earth)

Abstract The isostructural Ba2RIrO6 (R  La, Pr, Ho) perovskites have been characterized from X-ray diffraction data by means of the Rietveld method. They show an orthorhombic symmetry, space group Pbnm, with a random distribution of R and Ir cations in B sites. The magnetic properties of these materials have been studied via magnetic susceptibility measurements in the temperature range 4.2–300 K. Oxidation states of III were found for the rare earths and V for iridium when R  La and Ho, whereas in the case of Ba2PrIrO6 the oxidation state of both Pr and Ir was IV. The small value obtained for the effective magnetic moment of Pr(IV), i.e. 1.30 BM, has been explained in terms of crystal field effects; no magnetic interactions were detected.

Synthesis and structural characterization of a new perovskite series derived from LaNiO3: La5Ni4MO15(M Mo, Te, W)

The synthesis and crystal structure of the orthorhombic La5Ni4MO15(M Mo, Te, W) compounds are reported. These compounds can be regarded as being derived from LaNiO3 by substitution of 20% of Ni3+ by M6+ with the consequent reduction of some Ni3+ to Ni2+ Neutron, X-ray and electron diffraction data have established that these compounds are isostructural and have a distorted perovskite structure in which the cations placed in B sites are randomly distributed.

Synthesis, structural characterization and properties of solid solutions TiCuSbO with rutile structure

Abstract Solid solutions of stoichiometry Ti 1−x Cu x/3 Sb 2x/3 O 2 in the range 0.1 ≤ × ≤ 0.4 are obtained by thermal treatment of the appropriate amounts of simple oxides. These phases show a rutile-like structure in which Ti atoms are randomly substituted by Cu and Sb atoms in octahedral coordination of oxygen; the Jahn-Teller effect associated to Cu 2+ ions provokes an additions deformation of these octahedra, as afonction of the composition. Electron spin resonance and electrical conductivity measurements are also discussed.

Structural characterization and electrical behavior of LaNi1−xSbxO3 (0 ≤ x ≤ 13) perovskites

Abstract The structural and electrical characterization of the LaNi 1− x Sb x O 3 (0 ≤ x ≤ 1/3) perovskite-like system is reported. These compounds can be regarded as being derived from LaNiO 3 by partial substitution of Ni 3+ by Sb 5+ cations with the concomitant partial reduction of Ni 3+ to Ni 2+ . Perovskite-type structures with orthorhombic symmetry (S.G. Pbnm) have been found for all the series members with x ≠ 0, from X-ray diffraction. Resistivity and Seebeck measurements show the presence of metal to insulator (MI) transitions in these oxides.

Structural study and magnetic measurements of some perovskites MLnLiTeO6

Abstract The crystal structures of the perovskites MLnLiTeO6 (M=Ca, Sr and Ba) were determined from X-ray diffraction patterns. Rietveld analysis of the data gave at ambient temperature an ordered distribution of Li+ and Te6+ formal cations in B sites whereas the M2+ and Ln3+ cations occupy the A sites at random. Space groups and lattice parameters of these oxides are discussed on the basis of the distortions on the ideal perovskite structure. On the other hand, magnetic measurements are compatible with this distorted model in which paramagnetic cations are isolated.

Structural characterization and electronic properties of A-substituted LaNi0.8M0.2O3 (A = Ca, Sr; M = Te, W) perovskites

The synthesis, structural characterization and electronic properties of the A1 − xLaxNi0.8M0.2O3 (A = Ca, Sr; M = Te, W) perovskite-like system are reported. These compounds can be regarded as being derived from LaNiO3 by partial substitution in both the A and B sublatticcs of the perovskite structure: Ni3+ is substituted by M6+ cations and La3+ cations by divalent A ones. Orthorhombic symmetry (S.G. Pbnm) is found, from X-ray diffraction data, for all the title phases. Electrical resistivity measurements show semiconductor behavior in all cases (Ea < 0.2 eV). Ferromagnetic interactions with Curie temperatures ranging between 180 and 250 K are detected from susceptibility measurements.

Synthesis, structural characterization and properties of perovskite-type mixed oxides: BaLnBNiO6 (Ln=La,Nd; B=Sb,Nb,Ta)

Abstract The materials BaLnBNiO 6 (Ln=La, Nd; B=Sb, Nb, Ta) were obtained by thermal treatment of Ln(NO 3 ) 3 ·6H 2 O, BaCO 3 , NiCO 3 and B 2 O 5 in the temperature range 1473–1523 K. The crystal structure of BaNdSbNiO 6 was refined by the Rietveld analysis of powder X-ray diffraction data. The unit cell is related to a GdFeO 3 type perovskite with an ordered distribution of Sb and Ni ions (space group P 2 1 /n, a=5.679(1), b=5.677(2), c=8.045(4) A , β=89.8(1)∘;Z=2 . The electrical conductivities of BaNdBNiO 6 (B=Sb, Nb, Ta) have been measured over a wide temperature interval (300–1000°C). All these compounds are poor semiconductors. Magnetic susceptibility results suggest that none of these materials show long-range magnetic order in the temperature range measured.

Electronic properties of Ba2LnIrO6 (Ln = La, Ce, Pr, Eu, Ho, Er, Yb, Lu) perovskites

In the past few years the magnetic and electronic properties of iridium-containing perovskites have attracted considerable interest [1-6], because of the wide fange of variation giving behaviour ranging from semiconducting to metallic, frequently associated with cooperative magnetic properties. Special interest has been focused on the stabilization of unusual oxidation states of some transition-metal cations. In this context, various examples of perovskites in which the Ir s+ cation may be stabilized in an octahedral coordination have been reported [68]. The existence of some stoichiometric phases Ba2LnIrO 6 was initially reported by Thumm et al. [9] and the symmetry of these rare-earth mixed oxides was found to be cubic, whereas the indium analogue was hexagonal. More recently, Lang and Muller [10] have studied a hexagonal phase of a europium-containing perovskite. This letter reports the synthesis, structural characterization from powder X-ray diffraction (XRD) data and study of electronic properties, made from conductivity and Seebeck coefficient measurements, for Ba2LnIrO6 (Ln = La, Ce, Pr, Eu, Ho, Er, Yb, Lu) perovskites.