Cation Ordering Types and Dielectric Properties in the Complex Perovskite Ca(Ca{sub 1/3}Nb{sub 2/3})O{sub 3}

Journal Article · Mon Jan 01 04:00:00 EST 2001 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.2000.8971· OSTI ID:784335

Levin, I; Chan, J Y; Geyer, R G; Maslar, J E; Vanderah, T A

In the present work the effects of cation ordering on dielectric properties were isolated by investigating three polymorphs of Ca(Ca{sub 1/3}Nb{sub 2/3})O{sub 3} that feature different arrangements of the Ca{sup 2+} and Nb{sup 5+} cations on the B-sites of the perovskite structure. Dielectric measurements at frequencies above 1 GHz revealed a systematic dependence of the properties on the type of cation ordering. In particular, the structure with 2:1 ordering exhibited a lower dielectric constant and a significantly more negative temperature coefficient of resonance frequency than the structures with 1:1 and newly described k=1/4[1 1 1]*{sub c} ordering. Rietveld refinements of structural models for the three Ca{sub 4}Nb{sub 2}O{sub 9} polymorphs were conducted using X-ray and neutron powder diffraction data to elucidate structural details that could be correlated with the changes in dielectric properties. In all three polymorphs the cation ordering was combined with the same b{sup {minus}}b{sup {minus}}c{sup +} octahedral tilt system, and the structural refinements yielded similar magnitudes of the tilting angles. The most significant crystal-chemical difference between the three polymorphs was in the coordination environment of Nb{sup 5+}. Analysis of the refined bond distances indicated increasing average distortion of the Nb nearest-neighbor environment in going from the 1:1 to the k=1/4[1 1 1]*{sub c} to the 2:1 ordered structure. The increased fraction of strongly compressed Nb-O bonds in the 2:1 structure associated with the large distortion was correlated with the decrease in dielectric constant and more negative value of temperature coefficient of the resonant frequency obtained for this polymorph. Raman spectra obtained for the three polymorphs exhibited differences that were consistent with the observed structural chemistry.

• Research Organization: National Institute of Standards and Technology, Materials Science and Engineering Laboratory, Gaithersburg, Maryland (US); Electronics and Electrical Engineering Laboratory, Boulder, Colorado (US); Chemical Science and Technology Laboratory, Gaithersburg, Maryland (US)
• Sponsoring Organization: None (US)
• OSTI ID: 784335
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 156; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BOND LENGTHS
CALCIUM IONS
CALCIUM OXIDES
CATIONS
CHEMISTRY
DIELECTRIC MATERIALS
DIELECTRIC PROPERTIES
DIFFRACTION
EXPERIMENTAL DATA
GHZ RANGE
NEUTRON DIFFRACTION
NEUTRONS
NIOBIUM IONS
NIOBIUM OXIDES
PEROVSKITE
PEROVSKITES
RAMAN SPECTRA
RESONANCE
SPATIAL DISTRIBUTION
STRUCTURAL CHEMICAL ANALYSIS
STRUCTURAL MODELS
TEMPERATURE COEFFICIENT
TEMPERATURE DEPENDENCE
X-RAY DIFFRACTION