Preparation and crystal structure of H-BaTa{sub 2}O{sub 6}-type K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36} and dielectric properties of the related compounds

Journal Article · Tue Jul 12 00:00:00 EDT 2005 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2005.03.028· OSTI ID:20889800

Zhang, W ^[1]; Kumada, N ^[1]; Takei, T ^[1]; Yamanaka, J ^[1]; Kinomura, N ^[1]

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1. Center for Crystal Science and Technology, University of Yamanashi, Miyamae-7, Kofu, Yamanashi 400-8511 (Japan)

Single crystal of a novel compound, K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36}, has been synthesized in the course of investigation on the K{sub 2}O-BaO-Nb{sub 2}O{sub 5} system. The crystal structure was determined by single crystal X-ray diffraction data. The space group of this compound was found to be P6/mmm (no. 191) with the lattice parameters of a=21.109(4) and c=3.967(1)A. The final R-factors were R=0.039 and R{sub w}=0.042 for unique 508 reflections. The crystal structure had the same tunnel structure as that of hexagonal BaTa{sub 2}O{sub 6} (H-BaTa{sub 2}O{sub 6}), which is the high temperature form in three modifications of BaTa{sub 2}O{sub 6}. The chemical composition of K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36} was close to that of the tetragonal tungsten bronze (TTB) type KBa{sub 2}Nb{sub 5}O{sub 15} and the powder samples within this composition were prepared so as to clarify the boundary between H-BaTa{sub 2}O{sub 6} and TTB-type structures. The H-BaTa{sub 2}O{sub 6}-type structure appears in (K+Ba)/Nb-bar 0.500 and the TTB-type structure is in (K+Ba)/Nb>=0.575. The dielectric constants of these samples were measured from room temperature to 500deg. C for sintered body. The TTB-type compounds exhibited ferroelectric temperature dependence with the Curie points of 284-372deg. C and the H-BaTa{sub 2}O{sub 6}-type compounds were not ferroelectrics as predicted from the crystal structure analysis.

• OSTI ID: 20889800
• Journal Information: Materials Research Bulletin, Vol. 40, Issue 7; Other Information: DOI: 10.1016/j.materresbull.2005.03.028; PII: S0025-5408(05)00109-1; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BARIUM OXIDES
CHEMICAL COMPOSITION
CURIE POINT
FERROELECTRIC MATERIALS
HEXAGONAL LATTICES
LATTICE PARAMETERS
MONOCRYSTALS
NIOBATES
NIOBIUM OXIDES
PERMITTIVITY
POTASSIUM OXIDES
R FACTORS
SPACE GROUPS
TEMPERATURE DEPENDENCE
TUNGSTEN BRONZE
TUNNELS
X-RAY DIFFRACTION