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Ullah A.,University of Ulsan | Ahn C.W.,Convergence Components R and D Division | Lee S.Y.,University of Ulsan | Kim J.S.,University of Ulsan | Kim I.W.,University of Ulsan
Ceramics International | Year: 2012

Lead-free (1 - x)Bi 0.5(Na 0.78K 0.22) 0.5TiO 3-x(Bi 0.5La 0.5)AlO 3 (BNKT-BLA) piezoelectric ceramics with x ranging from 0 to 0.030 were synthesized by a conventional solid state reaction method. The effect of (Bi 0.5La 0.5)AlO 3 addition on the structure, ferroelectric properties, and electric field-induced strain were investigated. In the studied composition range, the XRD patterns revealed a single perovskite phase with tetragonal symmetry. However, the tetragonality (c/a) of the BNKT ceramics significantly decreased as the BLA content was increased. The polarization and strain hysteresis loops indicate that the ferroelectric order of the BNKT ceramics was significantly disrupted by the addition of BLA, leading to degradation in the remnant polarization and coercive field. However, the destabilization of the ferroelectric order is accompanied by significant enhancements in the bipolar and unipolar strains. A large electric field-induced strain (S = 0.40%) and a corresponding normalized strain (d33= Smax/ Emax=579pm/V) were observed under 70 kV/cm at a composition of x = 0.010. © 2011 Elsevier Ltd and Techna Group S.r.l. Source


Ullah A.,University of Ulsan | Ahn C.W.,Convergence Components R and D Division | Jang K.B.,University of Ulsan | Hussain A.,University of Ulsan | Kim I.W.,University of Ulsan
Ferroelectrics | Year: 2010

Lead-free piezoelectric (1-x)(Bi0.5Na0.5)TiO 3-xBiAlO3 (BNT-BA, x = 0.00, 0.025, 0.050, 0.075, 0.100) ceramics were synthesized by a conventional solid-state reaction method. The BNT-BA ceramics exhibited enhanced ferroelectric and piezoelectric properties at x = 0.050. The x-ray diffraction analysis revealed a pure perovskite phase for x ≤ 0.075. A rhombohedral to pseudocubic phase transition was observed at x = 0.075 and maximum values for the electric field-induced strain (S = 0.13%) and dynamic piezoelectric coefficient (d* 33 = 163 pm/V) were obtained at this composition. The enhancement in the electric field-induced strain is attributed to the rhombohedral to pseudocubic phase transition. © Taylor & Francis Group, LLC. Source


Hussain A.,University of Ulsan | Lee J.S.,University of Ulsan | Ahn C.W.,Convergence Components R and D Division | Kim J.S.,University of Ulsan | And 2 more authors.
Journal of the Korean Physical Society | Year: 2010

A lead-free piezoelectric 0.97Bi0.5(Na0.78K0.22)0.5TiO3-0.03(Na0.5K0.5)NbO3 (BNKTN-3) polycrystalline ceramic was synthesized by using a solid-state reaction method. X-ray diffraction (XRD) indicated the formation of a BNKTN-3 single phase having tetragonal symmetry. The temperature dependences of the dielectric properties of BNKTN-3 were investigated in the temperature range of 30 - 550 °C at various frequencies (0.01 kHz - 1 MHz), and its electrical properties were investigated by using complex impedance spectroscopy. Analyzing the complex impedance relaxation by using a Cole-Cole plot, we found the frequency dependence of the impedance relaxations to be one impedance arc in the complex impedance plot. The responses of electrical conduction are discussed in relation to grain effect upon equivalent circuit model. Source


Ahn C.W.,Convergence Components R and D Division | Hwang H.-I.,Convergence Components R and D Division | Lee K.S.,Inje University | Jin B.M.,Dong - Eui University | And 6 more authors.
Japanese Journal of Applied Physics | Year: 2010

We have fabricated K0.5Na0.5NbO3 (KNN) thin films on Pt substrates by a chemical solution deposition method and investigated the effect of K and Na excess (0-30 mol %) for KNN thin film. The KNN film with 20mol% excess K and Na was an optimized KNN perovskite phase. From the Raman spectra, a change in the scattering mode was observed due to the chemical composition fluctuations of the excess K and Na. The peak of the (v1 + v5) internal vibrational mode in the NbO6 octahedra was split into two vibration modes which were shifted toward lower or higher wavenumbers depending on the K and Na cation deficiencies or redundancies. © 2010 The Japan Society of Applied Physics. Source


Kim J.S.,University of Ulsan | Lee S.Y.,University of Ulsan | Ahn C.W.,Convergence Components R and D Division | Hwang H.I.,Convergence Components R and D Division | And 3 more authors.
Japanese Journal of Applied Physics | Year: 2010

K0.5Na0.5NbO3 thin films with (K,Na) excess and LiNbO3 substitution were fabricated on a Pt substrate by a chemical solution deposition method. The K0.5Na 0.5NbO3 thin films with (K,Na) 10 mol % excess and LiNbO3 5 mol% substitution showed a saturated ferroelectric polarization-electric field (P-E) hysteresis loop and the estimated remanent polarization (Pr) and coercive field (Ec) were 8.6 μC/cm2 and 40kV/cm at 280 kV/cm, respectively. Compared to pure K0.5Na0.5NbO3 thin films, the ferroelectric polarization of the thin film was improved and leakage current densities were decreased. Moreover, the ferroelectric polarization and leakage current characteristics are stable for higher applied electric fields and elevated temperatures. The conduction behaviours of these films were analyzed by Schottky and Poole-Frenkel emission. © 2010 The Japan Society of Applied Physics. Source

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