PREPARATION OF PEROVSKITE 0.75Pb(Ni1/3Nb2/3)O3-0.25PbTiO3 CERAMICS USING SEMICHEMICAL METHODS AND RELATED REACTION MECHANISMS

This article discusses a mechanism for preparing perovskite powders, 0.75Pb(Ni_1/3Nb_2/3)O₃-0.25PbTiO₃ (PNN-PT), using a semichemical method (SCM).Precursors were prepared by adding aqueous Ni(Ac)₂ solutions to an alcohol slurry of PbO, Nb₂O₅, and TiO₂. The TG-DTG and DSC analysis of the precursors and XRD analysis of the powders at different thermal treatment temperatures showed that the reaction mechanisms in this method differ from those in the conventional mixed-oxide method. The aqueous Ni(Ac)₂ solution reacted with PbO to form Pb(Ac)₂ · Pb(OH)₂ · H₂O and Ni(OH)₂, which decomposed to form nascent PbO and NiO, thereby improving the reactivity and distribution of PbO and NiO. Pb₃Nb₂O₈ and NiNb₂O₆ formed and were easily converted into the perovskite phase during the thermal treatment process. At a thermal treatment temperature of 850°C, the content of the perovskite phase reached 98%. Pyrochlore-free PNN-PT ceramic was obtained after 2 h of sintering at 1100°C, and its dielectric properties were found to be excellent at temperatures ranging between ?55 and 120°C.     

(1-x)Pb(Ni1/3 Nb2/3)O3-xPbTiO3陶瓷的合成及其电滞回线

采用两步法在850℃合成了(1-x)Pb(Ni1／3Nb2／3)O3-xPbTiO3(x=0．28～0．42)陶瓷,粉末均为单一钙钛矿相。扫描电子显微镜观察和介电性能检测表明：所研究的陶瓷的最佳烧结温度为1200℃。对1200C烧结的0．64Pb(Ni1/3Nb2/3)O3-0．36PbTiO3陶瓷的铁电性能进行了详细地研究,发现组成在准同型相界的陶瓷铁电性得到增强．而这种铁电性增强正是由组分及结构和准同型相界的本质共同决定的。     

Pb(Zn1/3Nb2/3)O3基复相陶瓷的室温介电老化行为

研究了Ｐｂ（Ｚｎ１／３Ｎｂ２／３）Ｏ３基复相陶瓷的室温介电老化行为与材料烧成制度的关系,性机和介电常数与老化时间的对数值成线性关系,随烧成温度提高和保温时间延长,老化速率增大,老化速率对频率的依存性增加。低温短时间烧结的复相陶瓷的介电老化行为类似于正常铁电体,其老化起因于畴壁运动;而高温长时间烧结的复相陶瓷表现为典型弛豫电体的老化行为,起因于缺陷偶极子与极性微区的相互作用。     

弛豫型铁电体Pb(B1/3Nb2/3)O3基复合陶瓷中两相共存的研究

在ＰＺＮ－ＢＴ,ＰＭＮ－ＢＴ－ＰＴ和ＰＮＮ－ＰＴ系统中,用两相混合烧结法,分别制备了ＰＺＮ基,ＰＭＮ基和ＰＮＮ基复合陶瓷,介电性能测试结果表明,ＰＺＮ基陶瓷为两相共存的复相陶瓷,而ＰＭＮ基和ＰＮＮ基陶瓷中的两相都发生了很大程度的固溶,应用键价理论和键性分析对此进行了讨论,并从两组元间扩散动力这的角度和显微结构特征对这一现象进行了分析。     

Preparation,structure, and electric properties of the Pb(Zn1/3Nb2/3)O3–Pb(Yb1/2Nb1/2)O3–PbTiO3 ternary ferroelectric system ceramics near the morphotropic phase boundary

Ceramics of the xPb(Zn_1/3Nb_2/3)O₃–(1 ? x ? y)Pb(Yb_1/2Nb_1/2)O₃–yPbTiO₃ (PZN–PYN–PT) ternary system were synthesized using a modified two-step columbite precursor method which can effectively suppress the pyrochlore phase. A morphotropic phase boundary (MPB) region, separating tetragonal and rhombohedral phases in the ternary systems has been determined. The electric properties of the compositions near MPB region were investigated. Dielectric response exhibits relaxor-like characteristics with broad dielectric peaks and dispersive dielectric behavior with respect to frequency and temperature. The phase diagram of the 0.45PZN–(0.55 ? y)PYN–yPT pseudo-binary system in the composition range of 0.15 < y < 0.35 was established based on dielectric measurements. The optimal properties were achieved in the MPB composition of 0.52PZN–0.21PYN–0.27PT with piezoelectric coefficient d₃₃, dielectric permittivity ε′, planar electromechanical coupling k_p, dielectric loss tan δ, coercive field E_c, remnant polarization P_r, and T_C being of 558 pC/N, 2065, 62%, 0.2%, 19.88 kV/cm, 31.44 μC/cm² and 259.5 °C, respectively, showing potential usage in high-temperature electromechanical applications.     

Composition-dependent electrical property of (1-x)Sr0.75Ba0.25Nb2O6-xPbZr0.52Ti0.48O3 solid solution ceramics

Solid solution ceramics of (1-x)Sr_0.75Ba_0.25Nb₂O₆-xPbZr_0.52Ti_0.48O₃ (x = 0?0.4) were prepared and investigated. The phase evolves from tungsten bronze for x = 0, coexisted tungsten bronze and pyrochlore at x = 0.3, to pyrochlore for x> 0.3. As the results, the ceramics show dramatically composition dependent microstructure and electrical property. The grain shape changes from anisotropic pillar-like with maximum length-diameter ratio of 3.3 at x = 0.2 to isotropic cubic-like for x> 0.2. At the same time, the maximum dielectric constant temperature tends to decrease with an exceptional increase at x = 0.3 due to the coexisted phases. Interestingly, the x = 0.3 ceramic endures ultrahigh breakdown strength of 340 kV/cm, which, together with enhanced polarization, results in maximum recoverable energy storage density of 3.0 J/cm³and energy storage efficiency of 81.5 % at room temperature.     

Temperature induced dielectric polarization evolution in polycrystalline Pb(Cd1/3Nb2/3)O3

The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometric and dielectric measurements performed for the same polycrystalline Pb(Cd_1/3Nb_2/3)O₃ (PCN) sample are presented. These results reveal the complex character of polycrystalline PCN dielectric properties; in particular, no structural phase transition (PT) was observed. The thermal expansion coefficient indicates glass-like behaviour of PCN. The frequency and temperature dependencies of complex dielectric permittivity were measured and analyzed in terms of diffused/relaxor transition of the ferroelectric polarization. Temperature induced evolution of the relative dielectric permittivity was found to involve two processes. Dielectric permittivity changes, originating from thermally induced evolution of thermal equilibrium of interactions between main structural lattice and two sub-lattices present in the sample were interpreted in terms of thermal evolution of polar cluster sizes in the region of relaxor/glass-like transition.     

PMN-PT系陶瓷的熔盐法合成及其压电性能研究

采用熔盐法合成在多晶相界附近的ＰＭＮ－ＰＴ系陶瓷样品,对其压电性能进行了研究,并与传统陶瓷工艺进行了比较．结果表明：熔盐法得到的样品的压电性能较好,Ｋｐ＝５８％,ｄ３３＝５２０ｐＣ／Ｎ;而传统陶瓷工艺得到的陶瓷样品的Ｋｐ＝４６％,ｄ３３＝３６７ｐＣ／Ｎ．采用ＳＥＭ和ＸＲＤ等手段对结果进行了分析和讨论．     

湿化学法制备0．95Pb（Mg_（1／3）Nb_（2／3））O_3－0．05PbTiO_3铁电陶瓷

用湿化学法制备了钙钛矿相的含量为９９％的０．９５Ｐｂ（Ｍｇ＿（１／３）Ｎｂ＿（２／３））Ｏ３－０．０５ＰｂＴｉＯ＿３（简称０．９５ＰＭＮ－０．０５ＰＴ）微粉，ＳＥＭ显示其粒度为０．２～０．３μｍ。通过ＸＲＤ确定了合成０．９５ＰＭＮ－０．０５ＰＴ前驱物的最佳条件为：溶液的ｐＨ值为１．５，反应温度为６０℃。制备０．９５ＰＭＮ－０．０５ＰＴ陶瓷时，预烧温度为８００℃（２ｈ），烧结温度为１２５０℃（１ｈ）。粉末烧结后制得纯钙钛矿相的０．９５ＰＭＮ－０．０５ＰＴ铁电陶瓷，其密度为理论密度的９５％，介电常数为１４８００（８００Ｈｚ）。     

Influence of external electric field on relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The effects of the external d.c. and a.c. electric field on the dielectric response and relaxor behaviour of lead–barium–zirconate–titanate (PBZT) ceramics of the composition Ba/Zr/Ti 25/70/30 have been studied. The significant influence of the strength of the d.c. bias field and the amplitude of the a.c. field on the dielectric constant maximum and frequency dispersion was determined. The magnitude of the dielectric response strongly decreases under the bias field and increases with the increase of the a.c. field amplitude. All parameters describing the relaxor behaviour of the studied ceramics changed under the external d.c. and a.c. electric field. The experimental results can be explained in terms of existing models of relaxors.     

Influence of lanthanum and niobium doping on the relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The lead–barium–zirconate–titanate (PBZT) ceramics of composition (Ba/Zr/Ti: 25/70/30) exhibit classical relaxor ferroelectric behaviour similar to other complex lead perovskites such as lead–lanthanum–zirconate–titanate or lead–magnesium–niobiate. Influence of Nb or La admixture on grain structure, dielectric and pyroelectric properties was showed earlier. The effect of simultaneously lanthanum and niobium modified PBZT 25/70/30 ceramics on properties have been studied and compared with earlier results. The influence of the additives on the values of characteristic parameters describing the relaxor behaviour of the studied ceramics (ε^′_max, T_m, T_f, T_B) was determined.     

Improving the energy storage performance of 0.88(Bi0.4Ba0.2Na0.2K0.2)TiO3–0.12Sr(Mg1/3Nb2/3)O3 high-entropy relaxor ceramics by AlN doping

In this study, we report the effects of AlN additives on the microstructure and energy performance of 0.88(Bi_0.4Ba_0.2Na_0.2K_0.2)TiO₃-0.12Sr(Mg_1/3Nb_2/3)O₃ high-entropy relaxor ceramics. We show that AlN partially reacts with/dissolves into the matrix and only forms a secondary phase when its concentration is above a threshold. AlN doping can only affect the shape of the P-E loop and improve the breakdown strength when it formed the secondary phase. The breakdown strength first increased and then decreased with increasing AlN concentration. When the AlN concentration is 6 mol%, the ceramic has the optimal energy storage performance with a breakdown electric field of 340 kV/cm, a recoverable energy density of 3.85 J/cm³, and an efficiency of 85.8%. The study suggests that the addition of AlN is an effective way to improve the energy storage performance of high-entropy ceramics.     

Enhanced energy storage properties of Bi(Ni2/3Nb1/6Ta1/6)O3–NaNbO3 solid solution lead-free ceramics

Sodium niobate energy storage ceramics with good environmental performance are widely used in electric power conversion and pulse power system, large energy storage density and high efficiency, huge power density and charge and discharge faster. In this work, (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/6Ta_1/6)O₃ [(1-x)NN-xBNNT] (0.12 ≤ x ≤ 0.18) ceramics system were prepared by solid state reaction method. By introducing Bi(Ni_2/3Nb_1/6Ta_1/6)O₃ (BNNT), a relaxation strategy was constructed, which significantly improved the energy storage properties of NaNbO₃ (NN) based ceramics. Finally, comparatively high recoverable energy density (W_rec) of 3.43 J/cm³ and large energy storage efficiency (η) of 83.3% were obtained in 0.86NN-0.14BNNT ceramics. Besides discharge energy density (W_d) of 0.69 J/cm³, ultra fast charge-discharge rate (t_0.9) of 55 ns, the power density (P_D) of 70.66 MW/cm³ and the current density (C_D) of 883.23 A/cm² were also observed in ceramic.     

Ferroelectric and electromechanical performance of diverse engineered states of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics

The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃ ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field E_i is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization P_D in aged samples can reverse the spontaneous polarization P_S back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented P_D and resulting E_i in poled-state samples will lead to the asymmetric loops and strain memory effect.     

Strain properties of (1-x)Bi0.5Na0.4K0.1TiO3-xBi(Mg2/3Ta1/3)O3 electroceramics

A ternary solid solution of Bi_0.5Na_0.5TiO₃–Bi_0.5K_0.5TiO₃–Bi(Mg_2/3Ta_1/3)O₃ (BNKT-xBMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (T_F-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d₃₃* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.     

Relaxor ferroelectric behaviour observed in (Ca0.5Sr0.5Ba0.5Pb0.5)Nb2O7 perovskite layered structure ceramics

Relaxor ferroelectric behaviour was observed in perovskite layered structure (PLS) (Ca_0.5Sr_0.5Ba_0.5Pb_0.5)Nb₂O₇ (CSBPN) ceramics engineered using the high entropy approach. The CSBPN ceramics were sintered at 1350 °C and are single-phase with an orthorhombic structure (Cmcm space group) at room temperature. Their relaxor ferroelectric behaviour is characterized by a broad and frequency-dependent permittivity maximum and a current peak around zero electric field in the hysteresis loop. The presence of polar nanoregions is supported by piezoresponse force microscopy images. The value of the relative permittivity ?′ = 130 at 1 kHz and room temperature is much larger than that for conventional PLS ceramics Sr₂Nb₂O₇ (?′ = 42) and Ca₂Nb₂O₇ (?′ = 38). This can be attributed to the presence of polar nanoregions and the lattice distortion effect in high entropy materials. The appealing dielectric and relaxor behaviour of CSBPN ceramics confirms the efficacy of the high entropy approach to obtain improved properties.     

先驱体法合成三元系Pb（Sc1／2Ta1／2）O3—PbZrO3—PbTiO3钙钛矿铁电陶瓷粉末

本文研究了采用不用先驱体ＳｃＴａＯ４＋Ｚｒ０．５３Ｔｉ０．４７Ｏ３（ＳＴ＋ＺＴ）和（Ｓｃ１２Ｔａ１２）０．２０Ｚｒ０．３８５Ｔｉ０．４１５Ｏ２（ＳＴＺＴ）以及采用ＳＴ＋ＺｒＯ２＋ＴｉＯ２与ＰｂＯ进行固相反应合成三元系Ｐｂ（Ｓｃ１２Ｔａ１２）０．２０－Ｚｒ０．３８５Ｔｉ０．４１５Ｏ３钙钛矿陶瓷粉末的合成机理。实验表明，两种先驱体均能与ＰｂＯ反应制得单相钙钛矿材料，合成过程中未发现焦绿石相。实验中发现，以ＳＴ＋ＺＴ为先驱体比ＳＴＺＴ先驱体更容易得到单相钙钛矿材料，其原因是ＺＴ先驱体对材料钙钛矿形成具有一定的促进作用。实验过程中发现试样随合成温度的变化有程度不同的膨胀现象，这种膨胀是采用先驱体法合成的钙钛矿粉末具有超细晶粒尺寸的主要原因。     

High electric field-induced strain properties in La-doped Pb(In1/2Nb1/2)O3–PbZrO3–PbTiO3 relaxor ferroelectric ceramics

Piezoelectric ceramics with high strain response and low hysteresis are highly in demand for high-performance actuator applications. Unfortunately, the trade-off relationship between large field-induced strain and low hysteresis in piezoelectric ceramics is a key challenge for designing high-performance piezoelectric actuators. Herein, ymol%La-doped 0.10 Pb(In_1/2Nb_1/2)O₃-xPbZrO₃-(0.90–x)PbTiO₃ [0.10PIN-xPZ-(0.90-x)PT: ymol%La] ternary relaxor ferroelectric ceramics were prepared by conventional solid-state reaction technique. Pb(In_1/2Nb_1/2)O₃ (PIN) as a relaxor end member was introduced into (Pb,La) (Zr,Ti)O₃ (PLZT) system to improve relaxor characteristics and strain properties. A giant strain of 0.23% was obtained in 0.10PIN-0.59PZ-0.31 PT: 8mol%La ceramic at the electric field of 20 kV/cm, with a high piezoelectric d₃₃* of 1150 pm/V and low hysteresis H_y of 6.4%, exhibiting a potential application in high-performance piezoelectric actuators. Furthermore, the effects of La ion doping and components on the ferroelectric, dielectric and electric field-induced strain properties were investigated, and provides a new way for improve the strain properties of piezoelectric materials.