Structural evolution of Na0.5K0.5NbO3 at high temperatures

Nobuo Ishizawa, Jun Wang, Terutoshi Sakakura, Yumi Inagaki, Ken Ichi Kakimoto

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)

Abstract

Changes in structure and dielectric properties at elevated temperatures have been investigated on single-crystals of sodium potassium niobate, Na 0.5K0.5NbO3, grown by the flux method. Single-crystal X-ray diffraction studies revealed that the crystals underwent orthorhombictetragonal and tetragonalcubic 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, 51 in tetragonal and 42 in orthorhombic. An Na atom occupied a slightly different position from the K atom in 12-fold coordination, resulting in fewer coordination numbers of 84 in cubic and tetragonal and 75 in orthorhombic. The spontaneous polarisation (Ps) estimated from the atom positions and formal charges were approximately 0.29 C m-2 in orthorhombic and 0.18 C m-2 in tetragonal. The contribution of the alkaline oxide components to Ps 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.

Original languageEnglish
Pages (from-to)2731-2738
Number of pages8
JournalJournal of Solid State Chemistry
Volume183
Issue number11
DOIs
Publication statusPublished - 2010 Nov 1
Externally publishedYes

Keywords

  • High temperature
  • NaKNbO
  • Phase transition
  • Single-crystal X-ray diffraction
  • Sodium potassium niobate
  • Spontaneous polarisation

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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