Y2O3 doped Ba0.9Ca0.1Ti0.9Sn0.1O3 ceramics with improved piezoelectric properties

Lead-free Ba_0.90Ca_0.10Ti_0.90Sn_0.10O₃-xY₂O₃ (BCTSY, x = 0–0.09) ceramics were prepared by traditional solid-state sintering method. All the BCTSY samples showed pure perovskite structures without detectable impurity. Orthorhombic/tetragonal phase coexisted in the sample of x = 0.03 to 0.07. Remarkable enhancement of the electric properties were achieved at x = 0.03 with d₃₃ of 650 pC/N, K_p of 59.6%, and the remnant polarization P_r of 10.2 μC/cm². The strengthened temperature stability of piezoelectricity is beneficial to the application of the piezoceramics.     

Dielectric properties and diffuse phase transition behavior of CuO-doped lead-free Ba(ZrxTi1−x)O3 ceramics

CuO-doped lead-free Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared through a solid state processing technique, and the effects of CuO on microstructure, dielectric properties and diffuse phase transition behavior were investigated. The average grain sizes were increased by CuO doping. The temperature and frequency dependences of the dielectric constant revealed that CuO-doped BZT20 ceramics exhibited broad diffuse phase transition behavior. The dielectric constant increased with increasing CuO concentration. The value of T_m and degree of diffusion (γ) changed regularly in the studied compositional ranges. The BZT20 samples with 1.0 mol% CuO doping, sintered at 1310 °C, showed excellent dielectric property and lower diffusivity with ε_m=21,371 and γ=1.87. These results can be explained by the disordered distribution of Cu ions in the B sites and the weakened bonding force with oxygen ions in Cu substituted BZT20 structure.     

Phase formation and electrical properties of Ba(ZrxTi1−x)O3 ceramics synthesized through a novel combustion technique

High quality Ba(Zr_xTi_1?x)O₃ (BZT, 0.025≤x≤0.150, step=0.025) ceramic has been prepared by the combustion technique. The raw materials were mixed with CH₄N₂O and calcined at 1000 °C and sintered at 1375 °C. For Ba(Zr_xTi_1?x)O₃ with x=0.025, the ceramics exhibited orthorhombic structure at room temperature. The crystal structure was transformed to rhombohedral, tetragonal and cubic phase, respectively with increasing zirconium content. The effect of x on dielectric properties has been studied intensively. It is found that the phase formation, which was affected from zirconium substitution, strongly influences the dielectric behavior. The rhombohedral phase decreases the maximum dielectric constant while the tetragonal phase enhances it. An extrapolation studied revealed the phase transition peaks merged into one peak at x ～0.094. The highest diffuseness constant of 1.95 was observed in BZT with 0.075 mol% zirconium. This was caused by the broadest dielectric peak of ferroelectric phase transition and the imminent diffusion between ferroelectric phase transition peak and Curie phase transition peak. The ferroelectric properties were sensitive to the phase exhibited in BZT system.     

Structure and electrical properties of PZT–PMS–PZN piezoelectric ceramics

The quaternary piezoelectric ceramics of Pb(Zr_0.52Ti_0.48)O₃–Pb(Mn_1/3Sb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃ (PZT–PMS–PZN) with different PZN contents were synthesized by molten salt synthesis (MSS). The influence of PZN content on phase structure, microstructure, dielectric and piezoelectric properties was investigated in detail. The results of X-ray diffraction (XRD) show that the phase structure of ceramics transforms from rhombohedral phase to tetragonal phase with the increasing of PZN content. The morphotropic phase boundary (MPB) of composition is located in the range of PZN content from 2 to 7 mol%. The grain size of the ceramics gradually decreases with the increasing of PZN content. Dielectric and piezoelectric properties of ceramics are significantly influenced by the PZN content. Ceramics sintered at 1150 °C with 5 mol% PZN achieve excellent properties, which are as follows: Q_m = 1381, K_p = 0.64, d₃₃ = 369pC/N, tan δ = 0.0044 and T_c = 275 °C. The PZT–PMS–PZN system is a promising material for high power piezoelectric transformers application.     

Structural,dielectric and ferroelectric properties of lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 ceramics prepared by Plasma Activated Sintering

Lead-free Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃ (BCZT) ceramics were prepared by Plasma Activated Sintering (PAS). The influence of PAS sintering temperature on the crystalline phase, microstructure, and, dielectric and ferroelectric properties of BCZT ceramics were studied. The phase structure of BCZT ceramics first changed from rhombohedral phase to the coexistence of rhombohedral and tetragonal phases and then to tetragonal phase as the sintering temperature increased. Microstructural characterization of BCZT ceramics indicated that PAS can obtain a compact microstructure at lower temperatures of 1150–1300 °C compared with that from common pressureless sintering. The BCZT ceramics showed different degrees of diffuseness with increased temperature, and the diffuseness exponents C are all approximately on the order of 10⁵ °C. The dielectric and ferroelectric properties of BCZT ceramics were enhanced with increased sintering temperature. BCZT ceramics sintered at 1250 °C exhibited optimum properties of room-temperature ε_r=2863, ε_m=6650, and 2P_r=25.24 μC/cm², resulting from the relatively higher tetragonal phase content of the MPB between tetragonal and rhombohedral phases together with a compact microstructure.     

Effect of Fe substitution on the piezoelectric,dielectric and ferroelectric properties of PNZST ceramics

Fe-doped (Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30)_0.52Ti_0.48]_0.98O₃ (PNZST) ceramics were prepared via conventional solid state reaction method, and the effect of Fe doping on their structural and electrical properties was investigated in detail. Results showed that Fe³⁺ cations could dissolve into readily the B-sites of perovskite structure for the PNZST ceramics with the less amount of Fe content (≤0.8 wt%), resulting in the full densification after sintered at 1300 °C. Meanwhile, Fe doping caused a structure transform from the tetragonal to the rhombohedral. The better electric properties for PNZST ceramic with 0.6 wt% Fe content were obtained, i.e. piezoelectric constant d₃₃=380 pC/N, electromechanical coupling factor k_p=0.57, mechanical quality factor Q_m=225, dielectric constant ε_r=1190, loss tangent tan δ=0.007 and curie temperature T_c=318 °C.     

Structural,piezoelectric and dielectric properties of PSLZT–PMnN ceramics

Pb_0.94Sr_0.05La_0.01(Zr_0.54Ti_0.46)_0.9975O₃–Pb(Mn_1/3Nb_2/3)O₃ (PSLZT–PMnN) ceramics with pure perovskite structure were prepared by conventional mixed oxide method. The influence of PMnN on the structural, dielectric and piezoelectric properties was investigated. The experimental results showed that the perovskite structure changed from tetragonal to rhombohedral symmetry and the Curie temperature decreased gradually with the increase of PMnN. The composition with 3 mol% PMnN exhibited favorable properties of Q_m (400), d₃₃(660 pC/N), k_p (0.60), K^T (1940), tan δ (0.90%) and T_C (247 °C), exhibiting potential usage for piezoelectric actuator and sensor applications.     

Microwave dielectric properties and microstructures of Nd(Mg0.5Sn0.5−xTix)O3 ceramics

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5Sn_0.5?xTi_x)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5Sn_0.5?xTi_x)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.5Sn_0.4Ti_0.1)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (?_r) of 21.1, a quality factor (Q × f) of 50,000 GHz, and a temperature coefficient of resonant frequency (τ_f) of ?60 ppm/°C were obtained for Nd(Mg_0.5Sn_0.4Ti_0.1)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Composition design,phase transitions and electrical properties of Sr2+-substituted xPZN–0.1PNN–(0.9−x)PZT piezoelectric ceramics

The influences of PZN content and Sr²⁺ substitution on the structure and electrical properties of Pb(Zn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (abbreviated as PZN–PNN–PZT) piezoelectric ceramics were studied. All as-prepared PZN–PNN–PZT ceramics presented single phase of perovskite structure, while higher PZN contents favored rhombohedral symmetry and larger grain size. Meanwhile, with the increase in Sr²⁺ content, the phase structure changed from a mix of tetragonal and rhombohedral symmetries to a pure rhombohedral symmetry. Although the ferroelectric Curie temperature (T_C) was decreased with increasing the PZN and Sr²⁺ contents, the piezoelectric constant (d₃₃) exhibited the opposite trend. As a result, optimum comprehensive electrical properties were obtained in the 0.1PZN–0.1PNN–0.8PZT composition with 10 mol% Sr²⁺ substitution: d₃₃~800 pC/N, k_p ~0.65, ɛ_r~4081, T_C~176 °C, P_r~30.92 µC/cm². Thus, the 10 mol% Sr²⁺-substituted 0.1PZN–0.1PNN–0.8PZT ceramic is a promising candidate for high performance applications.     

Enhanced electrical properties in lead-free NBT–BT ceramics by series ST substitution

Comprehensive electrical properties of 0.94(Na_1/2Bi_1/2)TiO₃–0.06BaTiO₃ lead-free ceramics by doping series SrTiO₃ were investigated. High piezoelectric constant of 205 pC/N and electromechanical coupling factor of 0.34 were obtained due to the forming of the rhombohedral–tetragonal morphotropic phase boundary at x=0.02–0.06. Very large recoverable strain of 0.34% was obtained at x=0.10 due to the coexistence of ferroelectric and relaxor pseudocubic phases. A large electrocaloric effect (ΔT_max=1.71 K and ΔT/ΔE=0.34 K mm kV⁻¹ at 50 kV cm⁻¹) which determined by indirect measurements method was obtained at 120 °C at x=0.02, which is significantly higher than that of lead-free ferroelectric ceramics reported so far. Moreover, lower operating temperatures of 50 °C and 30 °C were proposed when x=0.10 and 0.20 with ΔT_max=0.79 K and 0.6 K, respectively. These properties added together indicate a promising material for applications in cooling systems and actuators.     

A correlation between piezoelectric response and crystallographic structural parameter observed in lead-free (1-x)(Bi0.5Na0.5)TiO3–xSrTiO3 piezoelectrics

The structure of lead-free (1-x)(Bi_0.5Na_0.5)TiO₃-xSrTiO₃ (BNT-STx) ceramics was analyzed by the Rietveld method, using X-ray diffraction and neutron scattering data. The structural refinement results suggest that the crystal structure successively changes with SrTiO₃ concentration, x, from the rhombohedral phase (x = 0.00) to rhombohedral and tetragonal (x = 0.10–0.30), tetragonal and cubic (x = 0.40–0.60), and finally cubic (x = 0.80–1.00) phases. Correlation between the charge sensor constant (d₃₃) and the weighted off-center value (d_w) was observed, which may be attributed to the increased dipole motion in the unit cell due to an increased tendency to respond to external stimulation. Furthermore, an improved charge sensor constant (d₃₃) of 140 pC/N was observed for BNT-ST0.20, and a large strain of 0.25% and a d₃₃^* value of 443 pm/V were observed from x = 0.30.     

Barium modified lead lanthanum strontium zirconium niobium titanate for dielectric and piezoelectric properties

The isovalent Ba²⁺ modified lead lanthanum strontium zirconium niobium titanate (PLSZNT) solid solutions were prepared by solid-state reaction method with the compositional formula [Pb_{1−x−w−y}La_xSr_wBa_y][(Zr_zTi_1−z)_{(1−(x/4)−(5/4)k)}Nb_k]O₃ where Ba content, y, was varied from 0, 0.5, 1 and 1.5 mol%. X-ray diffraction (XRD) studies revealed that all the samples have ferroelectric tetragonal structure (FE_TET). The presence of multiple ions at Pb-site enhanced grain growth and further addition of Ba concentration resulted in restrained grain growth. Dielectric studies suggested that the ɛ_RT increased up to 1 mol% Ba while T_c has shown a continuous decreasing trend throughout the series. The piezoelectric parameters as a function of grain growth were characterized. The optimum piezoelectric charge coefficient (d₃₃ = 538 pC/N) and piezoelectric planar coupling coefficient (k_p = 0.521) was found to be in 1 mol% Ba modified PLSZNT ceramic, respectively, and this composition may be suitable for possible sensor and actuator applications.     

Morphotropic phase boundary and electrical properties of lead-free (K0.5Bi0.5)TiO3–Bi(Ni0.5Ti0.5)O3 relaxor ferroelectric ceramics

Lead-free relaxor ferroelectric ceramics (1?x)(K_0.5Bi_0.5)TiO₃–xBi(Ni_0.5Ti_0.5)O₃ were prepared by a conventional solid-state route, the phase transition behavior and corresponding electrical properties were investigated. A typical morphotropic phase boundary (MPB) between rhombohedral and tetragonal ferroelectric phases was identified to be in the range of 0.05<x<0.07 where the optimum piezoelectric and electromechanical properties of d₃₃=126 pC/N and k_P=18% were achieved. Most importantly, a high Curie temperature ~320 °C, around which the material shows a typical relaxor ferroelectric behavior characterized by the presence of diffuse phase transition and frequency dispersion, was obtained in MPB compositions, significantly higher than those of some existing MPB lead-free titanate systems. These results demonstrate a tremendous potential of the studied system for device applications.     

Crystal structure and microwave dielectric properties of Zn0.9Ti0.8−xSnxNb2.2O8 ceramics

The crystal structure and microwave dielectric properties of Zn_0.9Ti_0.8?xSn_xNb_2.2O₈ (x = 0.00, 0.05, 0.10, 0.15) ceramics sintered at temperatures ranging from 1100 °C to 1140 °C for 6 h were investigated. A single phase with ixiolite structure was obtained. With the increase of Sn content, the dielectric constant decreased attributed to the decrease of dielectric polarizability. The Qf value decreased with the decrease of packing fraction and grain size. The temperature coefficient of resonant frequency (τ_f) increased due to the increase of the bond valence of Zn_0.9Ti_0.8?xSn_xNb_2.2O₈ ceramics. The excellent microwave dielectric properties of ? = 35.05, Qf = 49,100 GHz, τ_f = ?27.6 × 10^?6/°C were obtained for Zn_0.9Ti_0.8?xSn_xNb_2.2O₈ (x = 0.05) specimens sintered at 1120 °C for 6 h.     

Effect of Ba0.85Ca0.15Ti0.90Zr0.10O3 content on the microstructure and electrical properties of Bi0.51(Na0.82K0.18) 0.50TiO3 ceramics

(1?x)Bi_0.51(Na_0.82K_0.18)_0.50TiO₃–xBa_0.85Ca_0.15Ti_0.90Zr_0.10O₃ [(1?x)BNKT–xBCTZ] ceramics were prepared by the conventional solid-state method, and the effect of BCTZ content on their microstructure and electrical properties was investigated. A stable solid solution with a pure perovskite phase is formed between BNKT and BCTZ, and these ceramics have a coexistence of rhombohedral and tetragonal phases in the range of 0 ≤ x < 0.15. Their T_m and T_d values are strongly independent on the BCTZ content. Moreover, the sintering temperature strongly affects the ferroelectric and piezoelectric properties of these ceramics with x = 0.02. These ceramics with x = 0.02 exhibit an optimum electrical behavior of d₃₃ ～ 205, k_p ～ 0.25, P_r ～ 31.8 μC/cm², and E_c ～ 19.1 kV/cm together with a high T_d value of ～91 °C when sintered at 1180 °C and poled at an optimum condition. As a result, the (1?x)BNKT–xBCTZ ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics prepared by Plasma Activated Sintering

Lead-free [Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃, BZT-xBCT] ceramics were prepared by Plasma Activated Sintering (PAS). The effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics was investigated. It was found PAS can obtain compact BZT-xBCT ceramics and BZT-0.50BCT ceramic possessed a MPB structure consisting of rhombohedral and tetragonal phases. Impedance spectroscopy confirmed two contributions from grains and grain boundaries, and the ceramics showed typical characteristic of diffuse phase transition. As compared with the BZT-xBCT ceramics with the pseudo-cubic phase, PAS-ed BZT-0.50BCT ceramic exhibited better properties of d₃₃ = 127 pC/N, k_p = 25.1%, ε_r = 2614, ε_m = 6655, and 2P_r = 25.2 μC/cm² due to the existence of the MPB structure.     

Effects of K nonstoichiometry in bismuth layer-structured K0.5+xBi4.5Ti4O15 ceramics

The effects of K nonstoichiometry on phase formation, grain morphology, dielectric and piezoelectric properties of K_0.5+xBi_4.5Ti₄O₁₅ (KBT) were studied in the range of excess up to +2 mol% and deficient down to ?8 mol% of K_0.5. The relative densities of the sintered KBT ceramics with various K contents prepared by a solid state reaction method were all higher than 95%. In all samples, a bismuth layer-structured phase was confirmed, although a secondary phase appeared as K deficiency became larger than ?6 mol%. Piezoelectric coefficient (d₃₃) increased, showing a high of 16 pC/N at x = ?3 mol%, and then decreased with further K deficiency while Curie temperature (T_C) decreased showing a low of 540 °C at x = ?8 mol% from 551 °C at x = 0 mol%. Mechanical quality factor (Q_m) of all samples was in the range of 900–1860.     

Dependence of dielectric properties on structural characteristics of (Zn1/3A2/3)0.5 (Ti1−xBx)0.5O2 (A = Nb5+, Ta5+, B = Ge4+, Sn4+) ceramics at microwave frequencies

The effects of structural characteristics on the dielectric properties of (Zn_1/3A_2/3)_0.5(Ti_1?xB_x)_0.5O₂ (A = Nb⁵⁺, Ta⁵⁺, B = Ge⁴⁺, Sn⁴⁺) (0.1 ≤ x ≤ 0.3) ceramics were investigated at microwave frequency. The sintered specimens showed solid solutions with a tetragonal rutile structure within the solid solution range of compositions. With an increase of BO₂, the temperature coefficient of resonant frequency (TCF) and dielectric constant (K) decreased with a decrease of oxygen octahedral distortion and dielectric polarizabilites, respectively. However, the quality factor (Qf) of the sintered specimens was increased with BO₂ due to the reduction of Ti⁴⁺ ions. The Qf value of the specimens with A = Ta was higher than that of the specimens with A = Nb.