A series of incommensurately modulated A{sub n}B{sub n}O{sub 3n+2} phases in the SrTiO{sub 3}-Sr{sub 2}Nb{sub 2}O{sub 7} quasibinary system

Journal Article · Sun Mar 01 04:00:00 EST 1998 · Materials Research Bulletin

DOI:https://doi.org/10.1016/S0025-5408(97)00245-6· OSTI ID:616347

Levin, I; Bendersky, L A; Vanderah, T A; Roth, R S ^[1]; Stafsudd, O M ^[2]

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1. National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Lab.
2. Univ. of California, Los Angeles, CA (United States). School of Engineering

A series of structurally related phases A{sub n}B{sub n}O{sub 3n+2} with A = Sr{sup 2+} and B = (Ti{sup 4+}, Nb{sup 5+}) have been prepared. Members of the homologous series with n = 4, 5, 6, 7, and noninteger values between 4 and 5 were characterized by high-resolution electron microscopy/transmission electron microscopy, bulk X-ray powder diffraction, and capacitive measurements of relative permittivities and their temperature coefficients. The structures of these compounds feature distorted perovskite-like slabs sliced parallel to the cubic (110) plane. For members of the series found at integral values, n indicates the width of the slabs (in number of [BO{sub 6}] octahedra). Samples at nonintegral values of n between 4 and 5 exhibited line structures, i.e., ordered intergrowths of the n = 4 and n = 5 structures. For these samples, n indicates the average width of the perovskite-like slabs. The compounds share a basic orthorhombic unit cell with a {approx} 3.9 {angstrom}, c {approx} 5.6 {angstrom}, and a long b dimension that increases incrementally as the width of the slabs increases. High resolution electron microscopy indicated that all of the compounds are incommensurately modulated along the shortest 3.9 {angstrom} cell dimension. The effects were not apparent in the bulk X-ray powder diffraction patterns. Experimental X-ray powder patterns indexed with the orthorhombic subcells are given for the new compounds with n = 4.33, 6, and 7. Preliminary capacitive measurements from 100 Hz to 5 MHz of relative permittivities and temperature coefficients indicated little frequency dependence but some unusual differences for successive members of the series, despite their crystal-chemical similarities.

• OSTI ID: 616347
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 3 Vol. 33; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CAPACITANCE
CRYSTAL STRUCTURE
ELECTRICAL PROPERTIES
NIOBIUM OXIDES
PERMITTIVITY
PHASE STUDIES
STRONTIUM OXIDES
TITANIUM OXIDES