Structural evolution of Na{sub 0.5}K{sub 0.5}NbO{sub 3} at high temperatures

Journal Article · Mon Nov 15 00:00:00 EST 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2010.09.018· OSTI ID:21494129

Ishizawa, Nobuo ^[1]; Wang, Jun; Sakakura, Terutoshi ^[1]; Inagaki, Yumi; Kakimoto, Ken-ichi ^[2]

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1. Ceramics Research Laboratory, Nagoya Institute of Technology, Asahigaoka, Tajimi 507-0071 (Japan)
2. Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

Changes in structure and dielectric properties at elevated temperatures have been investigated on single-crystals of sodium potassium niobate, Na{sub 0.5}K{sub 0.5}NbO{sub 3}, grown by the flux method. Single-crystal X-ray diffraction studies revealed that the crystals underwent orthorhombic-tetragonal and tetragonal-cubic phase transitions at 465 and 671 K during heating and 446 and 666 K during cooling, respectively. Both transitions were accompanied by volumetric discontinuities of collapse upon heating and expansion upon cooling, suggesting that the transitions were of the first order. The coordination numbers of an Nb showed a decreasing tendency with decreasing temperature, i.e., 6 in cubic, 5+1 in tetragonal and 4+2 in orthorhombic. An Na atom occupied a slightly different position from the K atom in 12-fold coordination, resulting in fewer coordination numbers of 8+4 in cubic and tetragonal and 7+5 in orthorhombic. The spontaneous polarisation (P{sub s}) estimated from the atom positions and formal charges were approximately 0.29 C m{sup -2} in orthorhombic and 0.18 C m{sup -2} in tetragonal. The contribution of the alkaline oxide components to P{sub s} was estimated to be approximately 15% in both ferroelectric forms. The temperature-induced transitions were also confirmed through the dielectric constant and dielectric loss at various frequencies and the differential scanning calorimetry. -- Graphical abstract: Changes in pseudocubic cell volume of an Na{sub 0.5}K{sub 0.5}NbO{sub 3} as a function of temperature; the inset is an enlargement near the transition between the orthorhombic and tetragonal forms. Display Omitted

• OSTI ID: 21494129
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 11; Other Information: DOI: 10.1016/j.jssc.2010.09.018; PII: S0022-4596(10)00412-3; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CALORIMETRY
COOLING
FERROELECTRIC MATERIALS
HEATING
MONOCRYSTALS
NIOBATES
ORTHORHOMBIC LATTICES
OXIDES
PERMITTIVITY
PHASE TRANSFORMATIONS
POLARIZATION
POTASSIUM COMPOUNDS
SODIUM COMPOUNDS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
X-RAY DIFFRACTION
ALKALI METAL COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTALS
DIELECTRIC MATERIALS
DIELECTRIC PROPERTIES
DIFFRACTION
ELECTRICAL PROPERTIES
MATERIALS
NIOBIUM COMPOUNDS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REFRACTORY METAL COMPOUNDS
SCATTERING
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS