Effect of potassium concentration on the structure and electrical properties of lead-free Bi0.5 (Na,K)0.5 TiO3–BiAlO3 piezoelectric ceramics (original) (raw)
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Current Applied Physics, 2010
Lead-free piezoelectric (1 À x)(Bi 0.5 (Na 0.78 K 0.22 ) 0.5 TiO 3 )-xBiAlO 3 (abbreviated BNKT22-BA, x = 0.00-0.100) ceramics were synthesized using a conventional sintering technique. The incorporation of BA into the BNKT22 lattice was investigated by X-ray diffraction (XRD), and the dielectric and ferroelectric characterizations and electric field-induced strain behavior. We found that the structural and electrical properties of BNKT22 ceramics are significantly influenced by the presence of BA content. X-ray diffraction revealed a pure perovskite phase for x 6 0.050. A phase transformation from tetragonal to pseudocubic was observed at x = 0.050. As BA content increased, the maximum dielectric constant continuously decreased, and the depolarization temperature (T d ) shifted towards lower temperatures. The polarization and strain hysteresis loops indicate that the addition of BA significantly disrupts the ferroelectric order. The destabilization of the ferroelectric order is accompanied by an enhancement of bipolar and unipolar strains. In particular, a very large electric field-induced strain (S = 0.35%) and a normalized strain (d à 33 = S max /E max = 592 pm/V) were observed at x = 0.030, near the tetragonal-pseudocubic phase boundary. These results suggested that the BNKT22-BA system is a promising candidate for high performance, lead-free electromechanical applications.
Electric-Field Induced Strain and Dielectric Properties of Pb(Mg1/3Nb2/3)O3-PbTiO3Ceramics
Ferroelectrics, 2015
The (1-x)Pb(Mg 1/3 Nb 2/3)O 3-xPbTiO 3 (PMN-PT) (0.10 x 0.35) ceramics were prepared by the columbite method. As the PT content increases, the ferroelectric state of PMN-PT system transforms gradually from the relaxor ferroelectric state to the normal ferroelectric state. The maximum electric-field induced strain reaches 0.25% at 32 kV/cm for the sample of x D 0.30 due to its piezoelectric character. The P-E loop, domain structure and dielectric property of (1-x)PMN-xPT clarify the contribution of domain to the large strain.
Solid State Communications, 2010
Lead-free perovskite solid solutions of (1 − x)(Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 )-xBiAlO 3 (abbreviated as BNKT20-BA, x = 0.00, 0.025, 0.050, 0.075, 0.100) were synthesized by a conventional solid state reaction method. XRD patterns revealed that a pure perovskite phase was formed for x ≤ 0.050. A structural transition from the coexistence of rhombohedral and tetragonal to pseudocubic phase was observed at x = 0.050. Polarization and strain hysteresis loops indicate that the ferroelectric order is disrupted significantly with the addition of BA. The destabilization of the ferroelectric order is accompanied by an enhancement of bipolar and unipolar strain. A large electric field-induced strain (S = 0.30%) and a normalized strain (d * 33 = S max /E max = 391 pm/V) were obtained at x = 0.050. These results provide evidence for the relation between the structural transition from the coexistence of rhombohedral and tetragonal into pseudocubic and the large electric field-induced strain in BNKT20-BA perovskite solid solutions.
Electronic Materials Letters, 2015
PZT-based ceramics have been the dominant piezoelectric material for a half century. They are widely used in various applications such as actuators, sensors and ultrasonic transducers. [1] The compositions near the morphotropic phase boundary (MPB) in PZT-based ceramics have attracted great attention because of their excellent electromechanical properties. [2] However, with the potential for regulations (RoHS/WEEE) that may restrict the use of hazardous substances in electronic devices, intensive efforts have been devoted to search for lead-free piezoelectric materials to serve as a substitute for PZT-based ceramics. In searching for high-performance lead-free piezoelectric ceramics, the MPB between two end members with different crystal structures has been one of the main strategies. Within the MPB region, maximum polarization values are attainable which leads to enhanced electrical properties. [2] Much attention has been paid to BNT-based solid solutions [3-7] Lead-free piezoelectric ceramics with compositions belonging to family of compositions (1-x)Bi0.5(Na0.80K0.20)0.5TiO3-xBa(Ti0.90Sn0.10)O3 or (1-x) BNKT-xBTS (when x = 0.05-0.15 mol fraction) near the morphotropic phase boundary (MPB) were fabricated by a conventional mixed oxide method. Sintered samples had relative densities greater than 98% of their theoretical values. X-ray diffraction data revealed that the MPB region consisted of coexisting rhombohedral and tetragonal phases in the BNKT-BTS system was identified over the entire compositional range. A large electric field-induced strain (Smax) of 0.36% and a normalized strain coefficient (d * 33) of 649 pm/V were observed in the BNKT-0.05BTS sample. The sample close to the MPB composition (BNKT-0.11BTS) exhibited the maximum dielectric constant (εr = 1770), temperature of maximum permittivity (Tm = 333C°) and lowfield piezoelectric coefficient (d33 = 227 pC/N), along with reasonable ferroelectric properties (Pr = 20.6 mC/cm 2 , Rsq = 0.88) and strain properties (d * 33 = 445 pm/V and Smax = 0.24%).
Physical Review B
K 0.5 Na 0.5 NbO 3 (KNN)-modified morphotropic phase boundary (MPB) compositions of the two Na 0.5 Bi 0.5 TiO 3-based lead-free piezoelectrics, namely, 0.94Na 0.5 Bi 0.5 TiO 3-0.06BaTiO 3 (NBT-6BT) and 0.80Na 0.5 Bi 0.5 TiO 3-0.20K 0.5 Bi 0.5 TiO 3 (NBT-20KBT) are model systems exhibiting large (>0.4%) electric-fielddriven strain. There is a general perception that (i) increasing KNN concentration monotonically weakens the direct piezoelectric response (d 33), and (ii) maximum electrostrain occurs when KNN pushes the system in the fully ergodic relaxor state. We have examined these issues using various complementary techniques involving electrostrain, piezoelectric coefficient (d 33), ferroelectric switching-current measurements, and field-driven structural studies on the global and local scales using laboratory and synchrotron x-ray diffraction, neutron powder diffraction, and Eu +3 photoluminescence techniques. Our investigations revealed the following important features: (i) In the low-concentration regime, KNN induces a tetragonal ferroelectric distortion, which improves the weak signal piezoresponse. (ii) Beyond a threshold concentration, in-phase octahedral tilt sets in and weakens the long-range ferroelectric order to partially stabilize an ergodic state. (iii) The maximum electrostrain (∼0.6%) is achieved in the mixed (nonergodic + ergodic) state. (iv) The mixed state invariably exhibits a less-known phenomenon of field-driven ferroelectric-to-relaxor transformation during bipolar field cycling. (v) The enhanced electrostrain in the mixed state is associated with the electric field increasing the correlation lengths of the short-ranged tetragonal and rhombohedral ferroelectric regions without overall transformation of one phase to the other. We summarize the findings of this work in a comprehensive electric field composition (E-x) phase diagram. The findings reported here are likely to be true for other NBT-based MPB systems.
Giant strain in Nb-doped Bi0.5(Na0.82K0.18)0.5TiO3 lead-free electromechanical ceramics
Materials Letters, 2010
The effect of Nb substitution on the crystal structure, ferroelectric, and electric field induced strain properties of Bi 0.5 (Na 82 K 0.18 ) 0.5 TiO 3 (BNKT) ceramics has been investigated. The coexistence of rhombohedral and tetragonal phases was found in undoped BNKT ceramics, however, Nb doping induced a phase transition to a pseudocubic phase with high electrostriction coefficients. When 3 mol% Nb was substituted on Ti ions, the electric field induced strain was markedly enhanced up to S max /E max = 641 pm/V, which is higher than those previously reported on non-textured lead-free electromechanical ceramics.
Ceramics International, 2012
Lead-free piezoelectric (1 À x)Bi 0.5 (Na 0.78 K 0.22) 0.5 TiO 3-xK 0.5 Na 0.5 NbO 3 (BNKT-xKNN, x = 0-0.10) ceramics were synthesized using a conventional, solid-state reaction method. The effect of KNN addition on BNKT ceramics was investigated through X-ray diffraction (XRD), dielectric, ferroelectric and electric field-induced strain characterizations. XRD revealed a pure perovskite phase with tetragonal symmetry in the studied composition range. As the KNN content increased, the depolarization temperature (T d) as well as maximum dielectric constant (e m) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 mC/cm 2) and small piezoelectric constant (27 pC/N) at 3 mol% KNN. As a result, at x = 0.03 a significant enhancement of 0.22% was observed in the electric field-induced strain, which corresponds to a normalized strain (S max /E max) of $434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature.
Electric-field-induced phase transition and large strain in lead-free Nb-doped BNKT-BST ceramics
Journal of the European Ceramic Society, 2014
A suite of Nb-based piezoelectric ceramics of 0.99[Bi 0.5 (Na 0.4 K 0.1)(Ti 1−x Nb x)]O 3-0.01(Ba 0.7 Sr 0.3)TiO 3 (BNKTN-BST), with x ranging from 0 to 0.030, was prepared by a conventional solid-state reaction method. X-ray diffraction patterns confirmed a single perovskite phase and the tetragonality was found to decrease with increasing Nb ratio. The BNKTN-BST ceramic had a high field-induced normalized strain coefficient of 634 pm/V at 2 mol% Nb content with a relatively small hysteresis compared with existing lead-free Bi-perovskite ceramics. An electric-fielddependent X-ray study was conducted to identify the main source of the high strain and ascertain the effect of electric fields on the crystal structure. The temperature-dependent P − E hysteresis loops of the BNKTN-BST ceramics were measured under an electric field of 60 kV/cm at various temperatures, and the effect of temperature on the ferroelectricity is discussed.
Ceramics International, 2012
Lead-free (1 À x)Bi 0.5 (Na 0.78 K 0.22) 0.5 TiO 3-x(Bi 0.5 La 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 0.5 La 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 (d à 33 ¼ S max =E max ¼ 579 pm=V) were observed under 70 kV/cm at a composition of x = 0.010.