Papers by Author: Chun Huy Wang

Abstract: Extending the investigations on (Na_0.5K_0.5)NbO₃-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Na_0.5K_0.5)NbO₃Bi_0.5(Na_0.90K_0.10)_0.5TiO₃ [NKN-BNK. (Na_0.5K_0.5)NbO₃ with 1 ~ 5 mol% Bi_0.5(Na_0.90K_0.10)_0.5TiO₃ has been prepared following the conventional mixed oxide process. It can be concluded that the NKN-BNKT ceramics have orthorhombic structures in the case x 0.03. With increasing BNKT content (x=0.04 to 0.05), however, the structure changes from orthorhombic to rhombohedral phase. Above results demonstrated that the MPB between orthorhombic and rhombohedral phases exits in the solid solution with the BNKT content of x=0.03. At the MPB composition, the cryctalline structure of ceramics is considered to be a coexistence of orthorhombic and rhombohedral phase. Owing to the phase coexistence at the phase boundary, there exists a different symmetry regions (DSR) near the MPB. The DSR boundary motion increases the dielectric permittivity and piezoelectric coefficients. The electromechanical coupling factor and dielectric constant are higher for compositions near the MPB. The dielectric constant (K^T₃₃), planar coupling coefficient (k_p), thickness coupling coefficient (k_t) and piezoelectric constant (d₃₃) of 0.98NKN-0.02BNKT ceramics were 1180, 30%, 58%, and 180, respectively.

Abstract: In the present study, various quantities of Bi₂O₃ were added into 0.98(Na_0.5K_0.5)NbO₃-0.02Bi(Na_0.93K_0.07)TiO₃ (0.98NKN-0.02BNKT) ceramics. It was found that 0.98NKN-0.02BNKT with the addition of 0~0.5 wt.% Bi₂O₃ exhibit relatively good piezoelectric properties. For 0.98NKN-0.02BNKT ceramics, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.40 and 0.47,respectively. For 0.98NKN-0.02BNKT ceramics with the addition of 0.3 wt.% Bi₂O₃, the electromechanical coupling coefficients ofthe planar mode k_p and the thickness mode k_t reach 0.50 and 0.53, respectively. It is obvious that 0.98NKN-0.02BNKT solid solution ceramics by adding low quantities of Bi₂O₃ is one of the promising lead-free ceramics for electromechanical transducer applications.

Abstract: In the present study, various quantities of Li2CO3 were added into Bi0.5(Na0.82K0.18)0.5TiO3 (abbreviated as 0.82BNT-0.18BKT) ceramics. For 0.82BNT-0.18BKT ceramics, the electromechanical coupling coefficients of the planar mode kp reaches 0.22 at the sintering of 1125 oC for 3 h. High-density samples were obtained through the addition of Li2CO3 into 0.82BNT-0.18BKT ceramics. It was found that 0.82BNT-0.18BKT with the addition of 0~0.9 wt.% Li2CO3 exhibit relatively good piezoelectric properties. For 0.82BNT-0.18BKT ceramics with the addition of 0.5 wt.% Li2CO3, the electromechanical coupling coefficients of the planar mode kp reach 0.37 at the sintering of 1125oC for 3 h. To promote the kp value, by adding low quantities of Li2CO3 is a effective method for 0.82BNT-0.18BKT solid solution ceramic.

Abstract: (Na0.5K0.5)NbO3 with Bi0.5(Na0.97K0.03)0.5TiO3 with x≤0.05 has been prepared by the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all the Bi(Na0.97K0.03)TiO3 diffuses into the lattice of (Na0.5K0.5)NbO3 to form a solid solution with a perovskite structure. A morphotropic phase boundary (MPB) between orthorhombic (O) and rhombohedral (R) was found at the composition 0.98(Na0.5K0.5)NbO3-0.02Bi0.5(Na0.97K0.03)0.5TiO3 [abbreviated as 0.98NKN-0.02BNKT] with correspondingly enhanced dielectric and piezoelectric properties. For 0.98NKN-0.02BNKT ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.33 and 0.49, respectively, after sintering at 1100 oC for 3 h. The ratio of the thickness coupling coefficient to the planar coupling coefficient is 1.48. With suitable Bi0.5(Na0.97K0.03)0.5TiO3 concentration, a dense microstructure and good electrical properties are obtained.

Abstract: Lead free piezoelectric ceramics 0.98(Na_0.5K_0.5)NbO₃-0.02(Na_0.5Bi_0.5)TiO₃ [abbreviated as 0.98NKN-0.02NB with the addition of 0~1.0 wt% Na₂CO₃ have been synthesized by the conventional mixed oxide process. The effects of amount of Na₂CO₃-content on the electrical properties and crystalline structures were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with Na₂CO₃ maintain an orthorhombic phase. In the case of low Na₂CO₃ content ( 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% Na₂CO₃, the electromechanical coupling coefficients of the thickness mode k_t and the planar mode k_p reach 0.51 and 0.33, respectively, after sintering at 1100 °C for 3 h. Moreover, the addition of excess Na₂CO₃ is a helpful method on ceramic processing to improve the dielectric tangent loss and the mechanical quality factor. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% Na₂CO₃ is a good lead-free piezoelectric ceramic.

Abstract: K2CO3-doped 0.98(Na0.5K0.5)NbO3-0.02(Na0.5Bi0.5)TiO3 [abbreviated as 0.98NKN-0.02NBT] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide process. The effects of K2CO3 additions on the crystalline structures and electrical properties of the 0.98NKN-0.02NBT ceramics were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with K2CO3 maintain an orthorhombic phase. In the case of low K2CO3 content (≤ 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% Na2CO3, the electromechanical coupling coefficients of the thickness mode kt and the planar mode kp reach 0.51 and 0.33, respectively, after sintering at 1100 oC for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% K2CO3 is a good lead-free piezoelectric ceramic.

Abstract: PbZrO3-PbTiO3 (PZT)-based ceramics are playing a dominant role in piezoelectric materials, their evaporation of harmful lead oxide during the sintering process causes a crucial environment problem. It is necessary to search for lead-free piezoelectric materials that have such excellent properties as those found in the PZT-based ceramics. Therefore (Na0.5K0.5)NbO3-based solid solutions were studied to improve piezoelectric properties. In the present study, various quantities of Bi2O3 were added into 0.98(Na0.5K0.5)NbO3-0.02Ba(Sn0.02Ti0.98)O3 (0.98NKN-0.02BST) ceramics. It was found that 0.98NKN-0.02BST with the addition of 0~4.0 wt.% Bi2O3 exhibit relatively good piezoelectric properties. For 0.98NKN-0.02BST ceramic with the addition of 1.0 wt.% Bi2O3, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.21 and 0.46, respectively, at the sintering of 1100oC for 3 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 2.2. It is obvious that 0.98NKN-0.02BST solid solution ceramic by adding low quantities of Bi2O3 is one of the promising lead-free ceramics for high frequency electromechanical transducer applications.

Abstract: Extending the investigations on (Na0.5K0.5)NbO3-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Na0.5K0.5)NbO3–Bi0.5(Na0.93K0.07)0.5TiO3 [NKN-BNKT]. (Na0.5K0.5)NbO3 with 2 ~ 6 mol% Bi0.5(Na0.93K0.07)0.5TiO3 has been prepared following the conventional mixed oxide process. A morphotropic phase boundary (MPB) between orthorhombic (O) and rhombohedral (R) was found at the composition 0.98NKN-0.02BNKT with correspondingly enhanced dielectric and piezoelectric properties. The electromechanical coupling factor and dielectric constant are higher for compositions near the MPB. The dielectric constant (KT33), planar coupling coefficient (kp) and thickness coupling coefficient (kt)of 0.98NKN-0.02BNKT ceramics were 1040, 47% and 48%, respectively.

Abstract: In the present study, various quantities of Bi₂O₃ were added into 0.98(Na_0.5Bi_0.5)TiO₃ -0.02Ba(Sn_0.08Ti_0.92)O₃ (0.98NBT-0.02BST) ceramics. High-density samples were obtained through the addition of Bi₂O₃ into 0.98NBT-0.02BST ceramic. It was found that 0.98NBT-0.02BST with the addition of 0~3.0 wt.% Bi₂O₃ exhibit relatively good piezoelectric properties. For 0.98NBT-0.02BST ceramic with the addition of 2 wt.% Bi₂O₃, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.12 and 0.61, respectively, at the sintering of 1100oC for 3 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 5.1. It is obvious that 0.98NBT-0.02BST solid solution ceramic by adding low quantities of Bi₂O₃ is one of the promising lead-free ceramics for high frequency electromechanical transducer applications.

Abstract: In this paper, (Na0.5Bi0.5)TiO3 -based solid solutions were studied to improve piezoelectric properties as those found in the PbZrO3-PbTiO3 (PZT)-based ceramics. The 0.98(Na0.5Bi0.5)TiO3 -0.02Ba(Sn0.08Ti0.92)O3 (0.98NBT-0.02BST) ceramics with the addition of 0~2.0 wt.% Nb2O5 have been prepared following the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all of the Ba(Sn0.08Ti0.92)O3 diffuse into the lattice of (Na0.5Bi0.5)TiO3 to form a solid solution, in which a hexagonal phase with a perovskite structure was found. For 0.98NBT-0.02BST ceramics with the addition of 0.5 wt.% Nb2O5, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.12 and 0.28, respectively, at the sintering of 1100oC for 3 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 2.3. It is obvious that 0.98NBT-0.02BST ceramics by adding low quantities of Nb2O5 are one of the promising lead-free ceramics for high frequency electromechanical transducer applications.