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Dive into the research topics where María Luisa Veiga is active.

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Featured researches published by María Luisa Veiga.


Journal of Materials Chemistry | 2002

Crystal and magnetic structure of the perovskites La2MTiO6(M = Co, Ni)

Elizabeth Rodríguez; María Luisa López; Javier Campo; María Luisa Veiga; C. Pico

The crystal structures of the perovskites La2MTiO6 n(M = Co and Ni) were determined on the basis of powder neutron diffraction data collected at room temperature. Refinements of the data showed that these compounds have monoclinic symmetry, space group P21/n, and the common structure is a perovskite-type with a partially ordered arrangement of M(II) and Ti(IV) cations on the 6-coordination sites. n Magnetic structures of type II have been determined from neutron diffraction data collected at 1.5 K and it was found that there was a long range antiferromagnetic ordering where only the M2+ ions are responsible for their magnetic properties. The antiferromagnetic ordering is explained by means of a propagation vector [k n= n½, 0, ½] and the respective magnetic moments at 1.5 K are 2.88 μB for nCo and 2.05 μB for Ni.


Materials Research Bulletin | 1988

Synthesis and magnetic properties of crystalline CrVO4

M.J. Isasi; R. Sáez-Puche; María Luisa Veiga; C. Pico; A. Jerez

Crystalline CrVO/sub 4/ was prepared by solid state reaction from Cr/sub 2/O/sub 3/ and V/sub 2/O/sub 5/ at 723 K. Their crystallographic parameters, and atomic positions were refined by the powder X-Ray method and their i.r. absorption bands were assigned. Magnetic properties were discussed on the basis of a 1D model.


Thermochimica Acta | 1987

A method for the kinetic analysis of nonisothermal decomposition reactions of solids

A. Jerez; Enrique Ramos; M. Gaitán; María Luisa Veiga; C. Pico

Abstract A new method, which allows the determination of the mechanism of a decomposition reaction of solids and leads to reliable kinetic parameters, is proposed. The test of the validity of the method is performed with seven simulated TG and DTG curves.


Journal of Solid State Chemistry | 1986

Synthesis, crystal structure, and some physico-chemical properties of Te3SeO8

C. Pico; A. Castro; María Luisa Veiga; Enrique Gutiérrez-Puebla; M.A. Monge; C. Ruiz-Valero

Abstract Monocrystals of a tellurium(IV) and selenium(IV) mixed oxide of composition Te3SeO8 have been prepared by solid state reaction between TeO3 and SeO2. The assignment of its IR absorption spectra has been achieved and its thermal decomposition process has been followed using TG and DSC techniques. The crystal structure of this new material has been determined by single crystal X-ray diffraction techniques: the compound has triclinic symmetry with lattice parameters: a = 4.854(1) A, b = 6.902(2) A, c = 11.515(2) A, α = 102.02(2)°, β = 100.80(1)°, and γ = 69.84(2)° (R = 0.027 for 1662 observed reflexions).


Journal of Alloys and Compounds | 1997

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

Inmaculada Mas Álvarez; María Luisa Veiga; C. Pico

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.


Journal of Materials Chemistry | 1994

Cation ordering in distorted perovskites (MLa)(MgTe)O6, M = Na, K

María Luisa López; María Luisa Veiga; C. Pico

The synthesis and crystal structure of the pseudo-orthorhombic (a≈b≈√2a0, c≈2a0) ordered perovskite MLaMgTeO6(M = Na and K) are reported. X-ray, electron and neutron diffraction and microscopy established that both compounds have a perovskite structure with ordering in the A and B sublattices.


Journal of Materials Chemistry | 1995

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

Inmaculada Mas Álvarez; María Luisa Veiga; C. Pico

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 and Reactivity in Inorganic and Metal-organic Chemistry | 1987

New Methods of Synthesis of Mixed Oxides of te and Pb: Characterization of the New Phases PbTeO3 (Cubic) and PbTeO4 (Orthorhombic)

M. Gaitán; A. Jerez; P. Noguerales; C. Pico; María Luisa Veiga

Abstract New methods of synthesis for mixed oxides of Te(IV) or Te(VI) and Pb(II) are described in this paper. The reactants were orthotelluric acid or tellurium trioxide, lead(II) acetate or hydrated oxide. The solid state reactions were carried out in air or in sealed tubes under vacuum. The isolated solid phases PbTeO3 (tetragonal and cubic), PbTeO3, Pb2Te3O8 and PbTeO4 were characterized by their X-ray diffraction powder patterns and by other techniques. Although some of these materials have been described previously, the experimental conditions employed in this work permit the isolation of some new phases.


Journal of Materials Chemistry | 1991

New antimonate–vanadate with the rutile structure

Josefa Isasi; María Luisa Veiga; A. Jerez; María Luisa López; C. Pico

VCrSbO6 has been prepared and its magnetic and electronic properties investigated. The crystal structure was refined from X-ray powder diffraction by the Rietveld method. The unit cell is tetragonal (space group P42/mnm, Z= 2), a= 4.5708(4)A and c= 3.0281(3)A. The compound is isostructural with the rutile phase FeNbO4 and stoichiometric with respect to all three constituent metals atoms. The electron diffraction pattern is consistent with a tetragonal symmetry.


Materials Research Bulletin | 1990

Dielectric response and ionic conductivity of Cs(NbTe)O6

Susana García-Martín; María Luisa Veiga; C. Pico; J. Santamaria; G. González-Díaz; F. Sánchez-Quesada

Abstract A study of the dielectric response in the frequency range 10 Hz to 10 7 Hz has been conducted on Cs(NbTe)O 6 defect pyrochlore oxides. Two different behaviours are identified: one characteristic of a volume conduction process by Cs + ions and other due to a contact effect. Ionic conductivity is derived from complex impedance plots and an activation energy of 0.67 eV is deduced for ion motion.

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C. Pico

Complutense University of Madrid

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A. Jerez

Complutense University of Madrid

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María Luisa López

Complutense University of Madrid

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M. Gaitán

Complutense University of Madrid

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Maria Angeles Arillo

Complutense University of Madrid

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I. Álvarez-Serrano

Complutense University of Madrid

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Susana García-Martín

Complutense University of Madrid

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Inmaculada Mas Álvarez

Complutense University of Madrid

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M. García-Hernández

Spanish National Research Council

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Martin Lopez

Complutense University of Madrid

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