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Abstract: Perovskite-type cobaltites LaCo1−x Mg x O3 (0< x ≤0.20) were synthesised by the liquid mix technique and structurally characterised by X-ray diffraction and neutron powder diffraction. This system can be regarded as LaCoO3-derived by means of partial substitution of trivalent cobalt ions by Mg2+. This doping is accompanied by the stabilization of the correspondent amount of Co4+ cations as it has been established from ICP, thermogravimetric and neutron diffraction results. The title materials behave as semiconductors up to 800K. Above this temperature they show a transition to the metallic state. Magnetic susceptibility and magnetization measurements show weak ferromagnetic interactions at 5K which has been interpreted taking into account disordered spin configurations for the cobalt cations. [Copyright &y& Elsevier]

Abstract: SrLaMnTiO6 orthorhombic perovskite has been synthesized by the liquid-mix technique. Structural characterization from X-ray and neutron diffraction shows a random distribution of Mn and Ti atoms. This material shows ferromagnetic ordering with a which can be interpreted in terms of a FM mode along y-axis. A M–I transition and a negative MR response of 90% have been detected at 210 K. AC and DC (ZFC and FC) magnetization measurements show an anomaly at low temperatures which has been attributed to effects of pinning of the FM domain walls rather than SG behaviour. Besides this, linear relation between coercitive field and is interpreted considering the existence of magnetic clusters of the same size embedded in a paramagnetic matrix. Finally the magnetocaloric properties of the title material have been studied and a discrete value of at RT has been found. [Copyright &y& Elsevier]

New phases which arise from partial substitution of Ti4+ by Cr3+ and Li+ of the compound La2/3TiO3 have been obtained, giving rise to the series La1.33LixCrxTi2−xO6 (x=0.66, 0.55 and 0.44). These phases adopt a perovskite-type structure as deduced from their structural characterization. Rietveld''s analyses of neutron diffraction data show that it is orthorhombic (S.G. Pbnm) with ordered domains. Conductivity has been examined by complex impedance spectroscopy and it increases with increasing lithium and chromium content. These materials behave as mixed conductors with low activation energies. Magnetic susceptibility variation with temperature shows antiferromagnetic interactions at the lowest temperatures. [Copyright &y& Elsevier]

The electroceramics of the x NaNbO 3 - (1-x) BiFeO 3 (x = 0.15, 0.25, 0.50, 0.75, 0.85, 1) system (NBNFO) have been prepared at moderate temperatures (600 °C). Microstructural analysis from high resolution electron microscopy reveals the existence of small crystals (10–150 nm), which agglomerate leading to micro-sized crystals. All the NBNFO compounds show perovskite-type structure and a transition from rhombohedral (S.G. R 3 c ) to orthorhombic (S. G. P 2 1 ma ) mean macroscopic symmetry takes place for x = 0.50, as analyzed by refinement of XRD data. Nevertheless, at the microstructural scale, the system can be described by a compositional-segregation picture in which structural heterogeneity is present. The materials show a positive temperature coefficient of resistivity (PTCR)-thermistor behavior above room temperature for x ≥ 0.50, up to maxima temperature values of 410, 393, 405 and 463 K for x values of 0.50, 0.75, 0.85 and 1, respectively. Above these temperatures, in the NTCR temperatures-region, conduction and polarization phenomena are analyzed from impedance and modulus formalisms in terms of two mechanisms implying different charge carriers: polaron hopping and/or diffusion of cation and oxygen vacancies. The activation energy values, E a , corresponding to these processes are of about 0.50 and 1 eV, respectively. Finally, in the dielectric response displayed by the NBNFO ceramics, the development of a FE contribution as x increases is detected, which can be interpreted considering microstructural features. [ABSTRACT FROM AUTHOR]

Thin films of SrBiMn 2-x Ti x O 6-δ have been fabricated by Pulsed Laser Deposition on SrTiO 3 [100] and [111] substrates. Their texture, width, homogeneity and morphology are evaluated by means of XRD, SEM, XPS, whereas complex impedance spectroscopy is employed to analyze their electrical response. The thickness values range between 80 and 900 nm depending on the experimental conditions. The epitaxial growing could be interpreted in terms of two contributions of microstructural origin: a matrix part and some polycrystalline surface formations (hemi-spheres). Texture studies suggest a fiber-type orientated morphology coherently with the Scanning Electron Microscopy images. XPS analyses indicate a segregation regarding A-sublattice cations, which features depend on the substrate orientation. This segregation could be connected to the development of nanopolar regions. Impedance data show the electrical polarization in the samples to be enhanced compared to bulk response of corresponding powdered samples. A relaxor behavior which fits a Vogel-Fulcher law is obtained for x = 0.50 whereas an almost frequency-independent relaxor ferroelectric behavior is registered for the thinnest film of x = 0.25 composition grown on SrTiO 3 [111] substrate. The influence of compositional and structural aspects in the obtained dielectric response is analyzed. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated SrLaMnTiO6 thin films by PLD on different substrates (SrTiO3, LaAlO3 and Si). Their texture, width, homogeneity and morphology have been evaluated from XRD, SEM and complex impedance spectroscopy. The thickness ranged between 500 and 8800nm depending on the synthesis conditions. The epitaxial growing could be interpreted in terms of two contributions of microstructural origin: a matrix part and some surface formations (hemi-spheres), with different texture and size distributions. The films were nanostructured and contained vertically aligned nanopores (VANPs) with a pore average size of 30–60nm, which are very interesting for eventual SOFC anode applications. Magnetization results indicate an improved response respect to nano-sized powder samples. [ABSTRACT FROM AUTHOR]

Polycrystalline Sr 2− x Bi x Ti 2− x Fe x O 6 ( x =0, 0.5, 1 and 1.5) perovskites have been synthesized by the ceramic method. Structural characterization from X-ray diffraction data showed that the symmetry evolves from centrosymmetric cubic ( Pm 3 ¯ m ) to non centrosymmetyric rhombohedral ( R3c ) as iron and bismuth content increase. For the intermediate composition, x =1, a mixed phase is obtained, which mean symmetry matches the best with the orthorhombic one ( Pbnm ). EDS analyses showed that the effective compositions differ from the nominal ones, and they were confirmed from Rietveld refinements of XRD data. HRTEM experiments indicated that in the case of x =1.5, a superstructure along [001] c and [111] c is observed. The dielectric response is modified depending on the composition range x . The x =0 compound shows a Debye type relaxation implying oxygen vacancy cluster, whereas a relaxor ferroelectric behavior is obtained for the x =0.5 and x =1 samples. Finally, in the case of x =1.5, the dielectric behaviour is characterized by strong dependence of permittivity with temperature. [ABSTRACT FROM AUTHOR]

Abstract: Microcrystalline powders of Sr1−x □ x LaMnTiO6−δ (0≤ x ≤0.15) perovskites have been synthesized by the sol–gel method. Structural characterization from neutron diffraction data shows tetragonal symmetry for all samples in the whole temperature range explored (5–700K) and HRTEM analysis confirms it at the micro scale. Structural refinements suggest that Sr/La and Mn/Ti cations are placed at random in A and B sublattices, respectively, being the vacancies exclusively located on the former sites. Doping with vacancies in the A sites does not provoke any extra structural ordering or distortion but modifies the electronic scenario at the B-sites, leading to an enhancement of Griffiths phase as the amount of vacancies, x, increases. Semiconductor behaviour has been observed, without any transition to metallic state, with typical activation energies of 0.15eV. The intrinsic magnetic frustrated behaviour is described in terms of a cluster-glass model. [Copyright &y& Elsevier]

Abstract: We report on the room temperature strong (∼80%) electroresistance (ER) in the double perovskite with mixed Mn valence: Sr2−x Gd x MnTiO6, 0≤ x ≤1. Both, continuous and pulsed current–voltage curves are almost identical which indicates that the observed electroresistance is not associated with heating. This is also supported by simultaneous temperature measurements. ER is negligible (absent) in the x =0 compound and increases with the increase of Gd content ‘x’. The amplitude of ER has a maximum for x =0.75, suggesting that ER is determined by both the double exchange and the Mn3+ concentration. At the same time, magnetic interactions change from the antiferromagnetic (x =0) to ferromagnetic ones as x →1, thus linking the ER with ferromagnetism. [Copyright &y& Elsevier]