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Author: search.filters.author.Sutapun, ManoonSubject: search.filters.subject.phase transition

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    CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics
    (2018-05-01)
    Sutapun, Manoon
    ;
    Charoonsuk, Thitirat
    ;
    Kolodiazhnyi, Taras
    ;
    Vittayakorn, Naratip
    The series of 0.86BaTiO<inf>3</inf>–(0.14−x)BaZrO<inf>3</inf>–xCaTiO<inf>3</inf> (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R-O and O-T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low-temperature dielectric loss peak was detected in the R phase at T = 90-150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel-Fulcher model with activation energy E<inf>a</inf> ≈ 60-300 meV and freezing temperature T<inf>VF</inf> ≈ 75-140 K. High piezoelectric strain coefficient (d<inf>33</inf>*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T<inf>C</inf>) was maintained at about 375 K.
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    Phase transition, dielectric and piezoelectric properties of lead-free piezoelectric (K1/2Na1/2)NbO3 - Bi(Zn2/3Nb1/3)O3 ceramics
    (2016-01-02)
    Sutapun, Manoon
    ;
    Muanghlua, Rangson
    ;
    Vittayakorn, Naratip
    The lead-free piezoelectric ceramics on the binary system of (1-x)(K<inf>1/2</inf>Na<inf>1/2</inf>)NbO<inf>3</inf>-xBi(Zn<inf>2/3</inf>Nb<inf>1/3</inf>)O<inf>3</inf> [(1-x)KNN-xBZnN]; x = 0.01-0.10 were fabricated by the solid state reaction method. The structure and phase transition were determined by X-ray diffraction.The results of XRD patterns suggested that Bi(Zn<inf>2/3</inf>Nb<inf>1/3</inf>)O<inf>3</inf> completely diffuse into the (K<inf>1/2</inf>Na<inf>1/2</inf>)NbO<inf>3</inf> lattices to form a solid solution. The crystal structure was in an orthorhombic phase for x ≤ 0.01. When reaching 0.01 < x ≤ 0.07, crystal structure became a rhombohedral phase and transformed to a pseudo-cubic structure for x > 0.07. The dielectric data shows that the amount of Bi(Zn<inf>2/3</inf>Nb<inf>1/3</inf>)O<inf>3</inf> added in the (K<inf>1/2</inf>Na<inf>1/2</inf>)NbO<inf>3</inf> decreases the ferroelectric - paraelectric transition temperature progressively. Furthermore, optimum piezoelectric and ferroelectric properties were observed at the composition, x = 0.01: effective piezoelectric coefficients (d<inf>33</inf>) = 498 pm/V, remanent polarization (P<inf>r</inf>) = 23.3 μC/cm<sup>2</sup>, coercive field (E<inf>c</inf>) = 14 kV/cm, maximum strain (Sma<inf>x</inf>) = 0.3% and Curie temperature (T<inf>C</inf>) = 380°C. The results of this study show that KNN with a small amount of Bi(Zn<inf>2/3</inf>Nb<inf>1/3</inf>)O<inf>3</inf> (x = 0.01) can be one of lead-free piezoelectric ceramic candidate.