We report the synthesis, the structural characterization, the ferroelectric behavior and the electronic properties of complex perovskite Ba2ZrTiO6. Samples of Ba2ZrTiO6 were synthesized through the standard solid state reaction method. The crystalline structure was studied by means of X-ray diffraction experiments and Rietveld-like analysis. Results reveal that the material crystallizes in a rhomboidal structure, space group R-3 (#148), with cell parameter a=5.8038(7) Å. The ferroelectric response of material was established from curves of polarization as a function of applied electric field. Our results reveal that the double perovskite Ba2ZrTiO6 has a ferroelectric hysteretic behavior at room temperature. The studies of the electronic structure show that Ba2ZrTiO6 behaves as a nonmetallic material with gap energy 2.32 eV. The structural parameters obtained from energy minimization, through the Murnaghan equation state are 99.5% in agreement with the experimental data

Deluque Toro, Críspulo Enrique

Landínez Téllez, David Arsenio

Roa Rojas, Jairo

DYNA

Spanish

En este trabajo reportamos la síntesis, la caracterización estructural, el comportamiento ferroeléctrico y las propiedades electrónicas de la perovskita compleja Ba2ZrTiO6. Las muestras fueron sintetizadas mediante el método estándar de reacción de estado sólido. La estructura cristalina se estudió a través de experimentos de difracción de rayos X y análisis de tipo Rietveld. Los resultados revelan que el material cristaliza en una estructura romboédrica, perteneciente al grupo espacial R-3 (#148), con un parámetro de red a= 5,8038(7) Å. La respuesta ferroeléctrica del material se estableció a partir de curvas de polarización en función del campo eléctrico aplicado. Nuestros resultados muestran que la perovskita Ba2ZrTiO6 evidencia un comportamiento histerético ferroeléctrico a temperatura ambiente. Los estudios de la estructura electrónica muestran que esta cerámica se comporta como un material no metálico con brecha de energía 2,32 eV. Los parámetros estructurales obtenidos a partir de la minimización de energía, a través de la ecuación de estado Murnaghan, son 99.5% acordes con los datos experimentales

DAVID A LANDÍNEZ-TÉLLEZ

CRÍSPULO ENRIQUE DELUQUE TORO

JAIRO ROA-ROJAS

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            Available in: http://www.redalyc.org/articulo.oa?id=49630072015  Red de Revistas Científicas de América Latina, el Caribe, España y PortugalSistema de Información CientíficaLANDÍNEZ-TÉLLEZ, DAVID A; DELUQUE TORO, CRÍSPULO ENRIQUE; ROA-ROJAS, JAIROELECTRONIC, STRUCTURAL AND FERROELECTRIC PROPERTIES OF THE Ba2ZrTiO6 DOUBLEPEROVSKITEDyna, vol. 81, núm. 183, febrero, 2014, pp. 126-131Universidad Nacional de ColombiaMedellín, Colombia   How to cite       Complete issue       More information about this article       Journal's homepageDyna,ISSN (Printed Version): 0012-7353dyna@unalmed.edu.coUniversidad Nacional de ColombiaColombiawww.redalyc.orgNon-Profit Academic Project, developed under the Open Acces InitiativeDyna, year 81, no. 183, pp. 126-131.  Medellin, February, 2014.  ISSN 0012-7353ELECTRONIC, STRUCTURAL AND FERROELECTRIC PROPERTIES OF THE Ba2ZrTiO6 DOUBLE PEROVSKITE PROPIEDADES ELECTRÓNICAS, ESTRUCTURALES Y FERROELÉCTRICAS DE LA DOBLE PEROVSKITA Ba2ZrTiO6 DAVID A. LANDÍNEZ-TÉLLEZPhD., Grupo de Física de Nuevos Materiales, Dep de Física, Universidad Nacional de Colombia, dalandinezt@unal.edu.co CRÍSPULO ENRIQUE DELUQUE TOROMs.C., Grupo de Nuevos Materiales, Universidad Popular del Cesar, Valledupar, deluquetoro@gmail.comJAIRO ROA-ROJASPhD., Grupo de Física de Nuevos Materiales, Dep de Física, Universidad Nacional de Colombia, Bogotá, jroar@unal.edu.coReceived for review November 08 th, 2012, accepted October 18th, 2013, final version December, 08 th, 2013ABSTRACT: We report the synthesis, the structural characterization, the ferroelectric behavior and the electronic properties of complex perovskite Ba2ZrTiO6. Samples of Ba2ZrTiO6 were synthesized through the standard solid state reaction method. The crystalline structure was studied by means of X-ray diffraction experiments and Rietveld-like analysis. Results reveal that the material crystallizes in a rhomboidal structure, space group R-3 (#148), with cell parameter a=5.8038(7) Å.  The ferroelectric response of material was established from curves of polarization as a function of applied electric field. Our results reveal that the double perovskite Ba2ZrTiO6 has a ferroelectric hysteretic behavior at room temperature. The studies of the electronic structure show that Ba2ZrTiO6 behaves as a nonmetallic material with gap energy 2.32 eV. The structural parameters obtained from energy minimization, through the Murnaghan equation state are 99.5% in agreement with the experimental data.Key words: Double perovskite, ferroelectric properties, electronic structureRESUMEN: En este trabajo reportamos la síntesis, la caracterización estructural, el comportamiento ferroeléctrico y las propiedades electrónicas de la perovskita compleja Ba2ZrTiO6. Las muestras fueron sintetizadas mediante el método estándar de reacción de estado sólido. La estructura cristalina se estudió a través de experimentos de difracción de rayos X y análisis de tipo Rietveld. Los resultados revelan que el material cristaliza en una estructura romboédrica, perteneciente al grupo espacial R-3 (#148), con un parámetro de red a= 5,8038(7) Å. La respuesta ferroeléctrica del material se estableció a partir de curvas de polarización en función del campo eléctrico aplicado. Nuestros resultados muestran que la perovskita Ba2ZrTiO6 evidencia un comportamiento histerético ferroeléctrico a temperatura ambiente. Los estudios de la estructura electrónica muestran que esta cerámica se comporta como un material no metálico con brecha de energía 2,32 eV. Los parámetros estructurales obtenidos a partir de la minimización de energía, a través de la ecuación de estado Murnaghan, son 99.5% acordes con los datos experimentales.Palabras clave: Perovskita compleja, propiedades ferroeléctricas, estructura electrónica1.  INTRODUCTION Complex perovskites with formula A2BB’X6, where A represents an alkaline earth, B and B’ are metal transition and X is the oxygen, have been studied because of their physical properties [1], which depend on structural distortions and the characteristic properties of B and B’ cations. This chemical configuration results in multiple opportunities to combine different elements of the periodic table, generating the possibility of synthesizing new materials that involve a larger gamma of physical properties. One well-known simple perovskite, which is well known because it exhibits a ferroelectric character, is BaTiO3 [2]. Partial substitutions of Ti by the Zr cation have been done by other authors, showing the evolution of the electric behavior from a ferroelectric response, for low concentration of Zr, to a ferroelectric relaxor [3] and a dielectric behavior for high concentrations of Zr [4]. However, the position of the substitutive cations in the crystallographic cell of the material is not usually reported. Location of all ions in the lattice is important for inferring the possibility of obtaining spontaneous polarization, in order to give rise to ferroelectric Landínez-Téllez et al / Dyna, year 81, no. 183, pp. 126-131, February, 2014. 127behavior. In the case of polycrystalline samples, the ferroelectric behavior depends greatly on the grain size, because the effects of imperfection frequently dominate the ferroelectric response of small grains, where a significant fraction of the material volume may be influenced by grain boundaries. It is known that cationic disorder produces substantial changes of the ferroelectricity of complex perovskites [5]. The aim of this paper is to show the synthesis process for producing the double perovskite Ba2ZrTiO6; to analyze the crystallographic single phase; to study the electronic structure; and, the most important objective of the study being to investigate the ferroelectric response of the material at room temperature. Our results reveal that Ba2ZrTiO6 crystallizes in a rhomboidal double perovskite structure, which is a convenient lattice for determining the occurrence the ferroelectric character, observed by the occurrence of hysteretic curves of electric polarization as a function of variable applied fields.2.  EXPERIMENTAL PROCESSSamples were synthesized by means of the solid state reaction recipe. The precursor powders BaCO3 (Aldrich 99.9%), TiO2 (Aldrich 99.99%) and ZrO2 (Aldrich 99.99%) were stoichiometrically mixed according to the chemical formula Ba2ZrTiO6. The mixture was ground to form pellets of 9.55 mm diameter and 1.85 mm thickness. Then the material was annealed in a sequential thermal procedure at 850, 900, 950, 1000, 1100 and 1150 ºC for 144 hours, including five regrinding and pelletizing procedures to make six thermal steps of 24 hours each. An X-Ray diffraction (XRD) experiment was performed by means of a PW1710 diffractometer with λCuKα=1.54064 Å. Rietveld refinement of the diffraction pattern was made by the GSAS code [6]. Electric polarization curves were obtained by means of a Radiant Ferroelectric Tester, which included a ±10 kV source for measurements in bulk-samples.3. CALCULATION METHODWe applied the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Kohn-Sham Density Functional Theory (DFT) [1], and adopted the Generalized Gradient (GGA) approximation for the exchange-correlation energy due to Perdew, Burke and Ernzerhof [7]. The self-consistent process was developed using the numeric package Wien2k [8]. Taking the experimental unit cell data as input, the structures studied in this work were fully relaxed with respect to their lattice parameters and the internal degrees of freedom compatible with the space group symmetry of the crystal structure. The resulting energies versus volume functions have been fitted to the equation of state due to Murnaghan [9] in order to obtain the minimum energy value, the bulk modulus, its pressure derivative and the equilibrium lattice parameters and associated volume. The muffin-tin radiuses used were 2.40, 1.74, 2.14 and 1.53 for Ba, Ti, Zr and O respectively, angular momentum up to l = 10 inside the muffin-tin sphere, a maximum vector in the reciprocal space of Gmax =12.0, RMT*Kmax = 7.0, and a mesh of 800 points in the first Brillouin zone (equivalent to a maximum of 85 k points in the irreducible Brillouin zone). Finally, the convergence criteria for the self-consistent calculation was 0.0001 Ry for the total energies, 0.0005 u.a. in the charge and 1.0 mRy/u.a. in the internal forces.4.  RESULTS AND DISCUSSIONFigure 1. Diffraction patterns showing results of thermal treatment for obtaining rhomboidal structure for the double perovskite Ba2TiZrO6.Landínez-Téllez et al / Dyna, year 81, no. 183, pp. 126-131, February, 2014. 128The sequence of crystallization obtained by the thermal process, described in the experimental setup, for Ba2TiZrO6 samples is shown in the diffraction patterns of Figure 1.  As shown in Figure 1, the fourth thermal step, at 1000 ºC, evidences the perovskite phase of Ba2TiZrO6. However, some incipient peaks corresponding to impurities are observed close to 24o. These impurities vanish after the last thermal treatment at 1150ºC. A rigorous Rietveld refinement from experimental data of the diffraction pattern reveals that crystallization of material occurs in a rhombohedral double perovskite, which belongs to the space group R-3 (#148). The difference between simulated and experimental patterns is shown in Figure 2. The lattice parameters obtained from the refinement process were a=5.803(8) Å; primitive vectors angle α=59.9675o.  This result is ∼ 98.5% in agreement with the value supplied by the Structure Prediction Diagnostic Software [10], which gives a=5.7177 Å.In Figure 2, the top plot represents experimental data, the middle plot is the simulated refined diffractogram, and the line at the bottom corresponds to the difference between experimental and simulated patterns. Indexes of crystallographic planes are indicated in figure 2. The parameters of refinement are: RF2=4.69 % and x2=2.26.Figure 2. Experimental and simulated diffraction patterns of Ba2TiZrO6 material after Rietveld refinement. The bottom line corresponds to the difference between experimental and theoretical diffractograms.Atomic positions and occupancies of ions in the structure are shown in table 1.Table 1: Atomic position for the rhomboidal structure of Ba2TiZrO6, obtained by Rietveld refinement of diffraction patterns through the GSAS code.Atom x y zBa 0.7558 0.7558 0.7558Ti 0.0000 0.0000 0.0000Zr 0.5000 0.5000 0.5000O 0.7745 0.7745 0.2255Ba 0.2442 0.2442 0.2442O 0.2255 0.7745 0.7745O 0.7745 0.2255 0.7745O 0.2255 0.2255 0.7745O 0.7745 0.2255 0.2255O 0.2255 0.7745 0.2255One important parameter in perovskite materials is the tolerance factor, which is related to the probability of the formation of octahedral coordination of B and B‘ cations with the oxygen anion. The tolerance factor calculated for Ba2TiZrO6 material was 1.0312. This value, above 1.0, suggests the possibility of obtaining spontaneous polarizations from structural distortions that give rise to the ferroelectric character in the simple perovskite BaTiO3 [11], for example.Figure 3. Ferroelectric hysteresis measured at ambient temperature for the perovskite Ba2TiZrO6, for several applied fields up to 2.16x104 V/cm.Another important characteristic for the possible application of the material in ferroelectric devices is the Landínez-Téllez et al / Dyna, year 81, no. 183, pp. 126-131, February, 2014. 129response to high applied fields.  In Figure 3 sequence of polarization for applied electric fields up to 22.5 kV/cm is shown.  As observed in Figure 3, for the higher applied field we determine a saturation polarization of 0.175 µC/cm2, in a curve with a remnant polarization of 0.3125 µC/cm2 and a coercive field of 12.0 kV/cm.   These values are in agreement with strong ferroelectric materials of the BaTiO3 family [12,13] that evidence polarization saturation, remnant polarization and coercive fields, which are appropriate for technological applications in ferroelectric memories.Figure 4 shows the optimization of energy as a function of volume. The minimum energy value is obtained for -42368.114575 Ry. The equilibrium volume is 945.7608 Bohr3, which corresponds with a lattice constant a=11.0206 Bohr [a=5.831(8)] with a volume modulus Bo=155.9553 GPa. The lattice parameter obtained from the GGA approximation is 99.5% in agreement with our experimental results. Figure 4. Calculated total energy as a function of volume and c/a factor for the Ba2TiZrO6 material Figure 5. Rhombohedral structure of the Ba2TiZrO6 perovskite for the R-3 space group.The difference between the two minimums is less than the convergence parameter. The minimums for the energy as a function of volume were obtained by adjusting Murnaghan’s state equation to the square points [9]. The rhombohedral structure obtained by both procedures, Rietveld refinement of diffraction patterns and theoretical minimization of energy by the DFT method, is shown in figure 5.Figure 6 corresponds to electronic properties of the perovskite Ba2TiZrO6. The Density of States (DOS) along the high symmetry directions in the first Brillouin zone and the band structure are shown. The energy of the electrons as a function of the wave vector k is also observed, which was taken along the Γ-Σ-M-K-Λ-Γ directions.  Figure 6. Band structure and total DOS for the Ba2TiZrO6 mate-rial. The Fermi level is the energy reference.The DOS and band structure are calculated for the equilibrium configuration by using the lattice constant corresponding to the volume which minimizes the energy of the system. The energy reference is selected to be the Fermi level in E=0. It is observed that the Ba2TiZrO6 material presents a nonmetallic behavior with a direct energy gap of 2,32 eV at the Fermi level.  Furthermore, a valence sub-band sited in the regime between -4 eV and the Fermi level is observed in Figure 6, due to principal contributions of the 2s-O, 3d-Ti and 4d-Zr orbital, as corroborated in Figure 7. A minority contribution of the 4s-Ti and 5s-Zr electrons is also observed. In the intermediate region Landínez-Téllez et al / Dyna, year 81, no. 183, pp. 126-131, February, 2014. 130of the conduction band, between 2,32 eV and 3,7 eV, the majority contribution is due to the 3d-Ti orbital. Figure 7. Partial DOS calculated for the Ba2TiZrO6 material.On the other hand, from 3,7 eV up to 4,71 eV a gap of forbidden energies, internal to the conduction band, is determined. Likewise, the 6s-Ba, 4d-Zr, 3d-Ti and 2p-O electron contributions give rise to the regime between 4,74 eV and 12,0 eV, with a small share of 4s-Ti, 5s-Zr and 2s-O orbitals.5.  CONCLUSIONSIn summary, we report the synthesis of polycrystalline Ba2TiZrO6 double perovskite.  The complete thermal process is seen through a sequence of diffraction patterns. Rietveld refinement reveals that a single crystallographic phase of rhombohedral perovskite was obtained, space group R-3 (#148), with lattice parameters a=5.803(8) Å.  The tolerance factor was calculated to be 1.03.  Measurements of polarization as a function of applied electric fields show a hysteretic behavior, which is characteristic of ferroelectric materials.  Values of saturation and remnant polarization suggest that this material may be used for technological applications in devices for information storage. Lastly, calculations of band and electronic structure reveal the nonmetallic behavior of Ba2TiZrO6, with an energy gap of 2.32 eV and Bo=155.9553 GPa volume modulus.6.  ACKNOWLEDGMENTSThis work was partially supported by the División de Investigaciones Sede Bogotá (DIB) of the Universidad Nacional de Colombia.REFERENCES[1] Palkar, V.R., Malik, S.K., Observation of magnetoelectric behavior at room temperature in Pb(FexTi1−x)O3, Solid State Communications 134, pp.783-786, 2005.[2] Landínez Téllez, D.A., Peña Rodríguez, G., Arbey Rodríguez, J., Fajardo, F., Roa Rojas, J., Structural, magnetic, multiferroic, and electronic properties of Sr2TiMnO6 double perovskite, Dyna 79, pp.111-115, 2012.[3] Isupov, V.A., Nature of physical phenomena in ferroelectric relaxors, Physics of the Solid State 45, pp. 1107-1111 (2003).[4] Baettig, P., Spaldin, N.A., Ab initio prediction of a multiferroic with large polarization, Applied Physics Letters 86, pp. 12505-12507, 2005.[5] Ang, C., Guo, R., Bhalla, A.S., Cross, L.E., Dielectric dispersion at microwave frequencies, Journal of Applied Physics 87, pp. 3937-3940, 2000.[6] Larson, A. C., Von, R. B., Dreele, General Structure Analysis System (GSAS), Los Alamos National Laboratory Report LAUR, pp. 86-748, 2000[7] Perdew, J.P., Burke, S., Ernzerhof, M., Generalized Gradient Approximation Made Simple, Physical Review Letters 77, pp. 3865, 1996.[8] Blaha, P., Schwarz, K., Madsen, G. K. H., Kvasnicka, D. and Luitz J., WIEN2k, An Aug-mented Plane Wave + Local Orbitals Program for Calculating Crystal Properties, Karlheinz Schwarz, Techn. Universitat Wien, Austria 2001, ISBN 3-9501031-1-2.[9] Murnaghan, F.D., The Compressibility of Media under Extreme Pressures, Proceedings of National  Academy of Sciences, USA. 30, pp. 244-247, 1944.[10] Lufaso, M.W., Woodward, P.M., The Prediction of the Crystal Structures of. Perovskites Using the Software Program SPuDS, Acta Crystallographic B 57, pp. 725-738, 2001.Landínez-Téllez et al / Dyna, year 81, no. 183, pp. 126-131, February, 2014. 131[11] Choi, K.J., Biegalski, M., Li, Y.L., Sharan, A., Schubert, J., Uecker, R., Reiche, P., Chen, Y.B., Pan, X.Q., Gopalan, V., Chen, Q., Schlom, D.G., Eom, C.B., Enhancement of ferroelectricity in strained BaTiO3 thin films, Science 306, pp. 1005-1009, 2004.[10] Hohenberg, P., Khon, W., Density Functional Theory, Physical Review 136, B864-B871, 1964.[12] D. Fu, M. Itoh, S. Koshihara, Lattice strain and polarization of the BaTiO3–CaTiO3 solid solution, Journal of Physics: Condensed Matter 22, 052204-052207, 2010.[13] Iijima, Y., Remanent polarization of vacuum-deposited BaTiO3 films, Electronics and Communications in Japan 68, pp. 27-35, 2007.

ELECTRONIC, STRUCTURAL AND FERROELECTRIC
PROPERTIES OF THE Ba2ZrTiO6 DOUBLE PEROVSKITE

Universidad Nacional De Colombia - Repositorio Institucional UN

Electronic, structural and ferroelectric properties of the ba2zrtio6 double perovskite

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

         Teléfonos:  3165000   Ext. 13032 / 13007   Fax  3165135 /3165000 Ext. 13083 A. A. : 5997 Bogotá, D.C.   Facultad de Ciencias Grupo de Física de Nuevos Materiales           Bogotá DC, 7 de octubre de 2012   Señores Comité Editorial REVISTA DYNA Facultad de Minas Universidad Nacional de Colombia Medellín   Respetados Señores  Les escribimos con el fin de solicitarles la evaluación para posterior publicación en la Revista DYNA, del artículo titulado ELECTRONIC, STRUCTURAL AND FERROELECTRIC PROPERTIES OF THE Ba2ZrTiO6 DOUBLE PEROVSKITE, para lo cual nos permitimos declarar lo siguiente: 1. Que es un trabajo original.  2. Que son titulares exclusivos de los derechos patrimoniales y morales de autor 3. Que los derechos sobre el manuscrito se encuentran libres de embargo, gravámenes, limitaciones o condiciones (resolutorias o de cualquier otro tipo), así como de cualquier circunstancia que afecte la libre disposición de los mismos 4. Que no ha sido previamente publicado en otro medio. 5. Que no ha sido remitido simultáneamente a otra publicación. 6. Que todos los autores hemos contribuido intelectualmente en su elaboración. 7. Que todos los autores hemos leído y aprobado la versión final del manuscrito remitido. 8. Que, en caso de ser publicado el artículo, transfieren todos los derechos de autor al editor, sin cuyo permiso expreso no podrá reproducirse ninguno de los materiales publicados en la misma.  Para el efecto, sugerimos los siguientes posibles evaluadores expertos en el tema:  NACIONALES Dr. Enrique Vera López, enrique.vera@uptc.edu.co, corrosion_total@yahoo.com, Escuela de Ingeniería, Universidad Pedagógica y Tecnológica de Colombia, Tunja Dr. Gabriel Peña Rodríguez, ggabrielp@yahoo.com, gpenaro@ufps.edu.co, Universidad Francisco de Paula Santander, Cúcuta. INTERNACIONALES Dr. Valdemar das Neves Vieira, valdemar_vieira@ufpel.edu.br, vdnvieira@gmail.com, Universidade Federal de pelotas, Brasil. Dr. Nelson Moreno Salazar, nomoreno@fisica.ufs.br, nomorenos@gmail.com, Universidade Federal da Paraíba, Brasil            Teléfonos:  3165000   Ext. 13032 / 13007   Fax  3165135 /3165000 Ext. 13083 A. A. : 5997 Bogotá, D.C.   Facultad de Ciencias Grupo de Física de Nuevos Materiales     Agradeciendo su atención y gentileza,          Cordialmente,                                                             Jairo Roa-Rojas, Ph.D.  David A. Landínez T., Ph.D.  Críspulo Deluque T., Ph.D.    

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Electronic, structural and ferroelectric properties of the ba2zrtio6 double perovskite

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