Layered-structural monoclinic–orthorhombic perovskite La{sub 2}Ti{sub 2}O{sub 7} to orthorhombic LaTiO{sub 3} phase transition and their microstructure characterization

Journal Article · Sat Mar 01 00:00:00 EST 2014 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2013.12.013· OSTI ID:22340331

Jiménez-Mier, J. ^[1]; Chavira, E. ^[2]

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1. Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 México D. F. (Mexico)
2. Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, 04510 México D. F. (Mexico)

The layered-structural ceramics, such as lanthanum titanate (La{sub 2}Ti{sub 2}O{sub 7}), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La{sub 2}Ti{sub 2}O{sub 7} ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by the sol–gel acrylamide polymerization route. The characterizations of the samples were achieved by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). X-ray diffraction indicates that the formation of monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} nanocrystals is a necessary first step to obtain orthorhombic LaTiO{sub 3} nanocomposites (with space group Pbnm). In this work we identified that the monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} with space group P2{sub 1} transforms its structure into one with the orthorhombic space group Cmc2{sub 1} at approximately 1073 K. The microstructure associated consisted of flaky monoclinic La{sub 2}Ti{sub 2}O{sub 7} nanocomposites in comparison with round-shaped LaTiO{sub 3} nanocomposites. - Highlights: • The flaky-like La{sub 2}Ti{sub 2}O{sub 7} compound was synthesized by sol–gel acrylamide route. • Simultaneous monitoring of the DTA and XRD with temperature was performed. • Phase transformation characterization of La{sub 2}Ti{sub 2}O{sub 7} has been carried out. • The variation of the La{sub 2}Ti{sub 2}O{sub 7} and LaTiO{sub 3} grain morphology has been compared.

• OSTI ID: 22340331
• Journal Information: Materials Characterization, Vol. 89; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
ACRYLAMIDE
ATOMIC FORCE MICROSCOPY
CERAMICS
DIELECTRIC MATERIALS
DIFFERENTIAL THERMAL ANALYSIS
LANTHANUM
LANTHANUM COMPOUNDS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MONOCLINIC LATTICES
NANOCOMPOSITES
ORTHORHOMBIC LATTICES
PEROVSKITE
PHASE TRANSFORMATIONS
POLYMERIZATION
SCANNING ELECTRON MICROSCOPY
SPACE GROUPS
TITANATES
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION