The symmetric studies on the structure-property relationship of the unpoled and poled states of 0.67BiFeO3-0.33BaTiO3 (0.67BF-0.33BT) were conducted to understand the origin of the morphotropic phase boundary (MPB) in BF-BT. A typical relaxor-type dielectric anomaly was observed (Tf, ~627 K). The remnant polarization (Pr) and maximum value of electro-strain (Sm) increase clearly during heating (Pr, ~40 uC/cm2; Sm, 0.191 % under 40 kV/cm at 453 K). The first-cycle electro-strain loops indicate the difference in the polar state between 0.67BF-0.33BT and 0.94BiNaTiO3-0.06BaTiO3. Both the unpoled and poled samples have the similar frequency dispersion behaviors. Even in the poled samples, the transition between the ergodic relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly. Analyses based on the Rietveld refinement of XRD patterns, bright-field images and selected-area electron diffractions (SAED) demonstrated that the formation of the long-range ferroelectric domains was difficult under the poling field.
Symmetry of high-piezoelectric Pb-based complex perovskites at the morphotropic phase boundary I. Neutron diffraction study on Pb(Zn1/3Nb2/3)O3 -9%PbTiO3
用中子衍射方法研究了Pb(Zn 1/3 Nb 2/3)O3 - 9%PbTiO3(PZN/9 PT)晶体的对称性,PZN/9 PT晶体的组成位于Pb(Zn 1/3 Nb 2/3)O3和PbTiO 3之间的准同型相界(MPB)。并与其他成分相同但史前史不同的标本进行了比较。所有试样的平衡态都不是端元菱方相和四方相的混合物,而是存在于一条新的极化旋转线Mc#(正交-单斜线)上。在所检查的样品中,一个在室温下表现出四方对称性,但在冷却和加热循环后恢复单斜相。
Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution: A Rietveld study
我们在这里提出的多铁性(1-x)Bi(Ni 1/2 Ti 1/2)O3-xPbTiO 3固溶体的结构研究的结果,使用Rietveld分析的粉末X射线衍射数据的组成范围为0.35至0.55。我们精确地测定了(1-x)Bi(Ni_(1/2)Ti_(1/2))O_(3-x)PbTiO_3在室温下的稳定区。通过划分准同型相界的相共存区,观察到了从准立方相到四元相的结构转变。准同型相界区由四斜晶系和单斜晶系共存的结构组成,空间群分别为P4 mm和Pm,Rietveld分析证实其组成范围为0.41 ~ 0.49。Rietveld分析的结果完全排除了早期工作者报道的在准同型相边界区菱面体相和四面体相共存的可能性。Rietveld精化后得到的B-位阳离子-氧阴离子的键长与使用Shannon-Prewitt离子半径计算的键长之间的比较,揭示了立方相的B-O键的离子性质和其他结晶相的部分共价特征。
Predicting morphotropic phase boundary locations and transition temperatures in Pb- and Bi-based perovskite solid solutions from crystal chemical data and first-principles calculations
使用从第一性原理计算获得的数据,我们表明,准同型相界(MPB)的位置和转变温度在MPB的铁电钙钛矿解决方案可以预测与定量准确性的组成阳离子的属性。通过密度泛函理论计算发现,Pb(B $'$ B $''$)O $_3$ -PbTiO $_3$,BiBO $_3$-PbTiO $_3$和Bi(B $'$ B $''$)O $_3$ -PbTiO $_3$中PbTiO $_3$在MPB处的摩尔分数与B阳离子的离子尺寸(容差因子)和离子位移呈线性关系.这种依赖性是由于局部排斥和A-阳离子位移排列相互作用之间的竞争。包含第一原理位移数据也允许在MPB的过渡温度的准确预测。得到的结构-性能的相关性被用来预测准同型相界和转变温度在尚未合成的固溶体。
Structural heterogeneity and diffuse scattering in morphotropic lead zirconate-titanate single crystals
本文报道了在准同型相界(x=0.475)附近组成的锆钛酸铅单晶体的同步辐射X射线漫散射和非弹性散射测量结果。在293 K < T < 400 K的温度范围内,观察到了高度各向异性的准弹性漫散射。在400 K以上,这种散射消失。它的主要特征可以再现的不均匀晶格变形所造成的四面体相到菱面体或单斜相的夹杂物的模型。这一观察结果支持了PZT在其准同型相界基本上是结构不均匀的想法。
Evidence of field induced inter-ferroelectric transformation as the dominant driving mechanism for anomalous piezoresponse in the morphotropic phase boundary piezoelectric system PbTiO3-BiScO3
Phase Coexistence and the Structure of the Morphotropic Phase Boundary Region in (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 Piezoceramics
研究了(1-x)Bi(Mg_(1/2)Zr_(1/2))O_(3-x)PbTiO_3陶瓷的准同型相结构和相共存区。结构是立方的,空间群为Pm 3 m,x为<0.57 and tetragonal with space group P4mm for the compositions with x>0.59。对于0.56<x<0.60的组分,四方相和立方相共存,这表明组分宽度Δx~0.03的非常窄的准同型相界区域。使用X射线衍射数据的结构的Rietveld精修证实了MPB区域中的四面体和立方相的共存,并且排除了早期工作者报道的四面体和菱形结构的共存。极化后立方相(x=0.55,0.56)的机电耦合系数出现显著值,表明存在电场诱导的中心对称立方相向非中心对称相的转变。极化-电场磁滞回线测量的立方组成(x=0.56)给出了良好的饱和回线类似于观察到的Pb(Mg_(1/3)Nb_(2/3))O_3弛豫低于冻结温度。
Sm-doped BiFeO3 compacted powders with composition across the morphotropic phase boundary region were prepared by sol-gel method. Crystal structure, morphology and magnetic state of the compounds were analyzed as a function of dopant concentration, temperature and external pressure using synchrotron and laboratory X-ray diffraction, electron microscopy, Raman and Mossbauer spectroscopy. Application of external pressure shifts the phase transition from the rhombohedral structure to the nonpolar orthorhombic structure towards lower concentration of the dopant content, wherein the amount of the a…
Samarium substituted bismuth ferrite (BiFeO3) ceramics prepared by sol-gel synthesis method were studied using both local scale and microscopic measurement techniques in order to clarify an evolution of the crystal structure of the compounds across the morphotropic phase boundary region. X-ray diffraction analysis, transmission and scanning electron microscopies, XPS, EDS/EDX experiments and piezoresponse force microscopy were used to study the structural transitions from the polar active rhombohedral phase to the anti-polar orthorhombic phase and then to the non-polar orthorhombic phase, obse…
Morphotropic phase boundaries (MPBs) show substantial piezoelectric and dielectric responses, which have practical applications. The predicted existence of MPB in HfO2-ZrO2 solid solution thin film has provided a new way to increase the dielectric properties of a silicon-compatible device. Here, we present a new fabrication design by which the density of MPB and consequently the dielectric constant of HfO2-ZrO2 thin film was considerably increased. The density of MPB was controlled by fabrication of a 10-nm [1 nm-Hf0.5Zr0.5O2 (Ferroelectric)/1 nm-ZrO2 (Antiferroelectric)] nanolaminate followed…
Recently, based on the phase-field modeling, it was predicted that Hf1-xZrxO2 (HZO) exhibits the morphotropic phase boundary (MPB) in its compositional phase diagram. Here, we investigate the effect of structural changes between tetragonal (t) and orthorhombic (o) phases on the ferroelectric and dielectric properties of HZO films to probe the existence of MPB region. The structural analysis show that by adjusting the ozone dosage during the atomic layer deposition process and annealing conditions, different ratios of t- to o-phases (f_(t/o) ) were achieved which consequently affect the ferroel…
Two-dimensional polarity is intriguing but remains in the early stage. Here a structural evolution diagram is established for GeS monolayer, which leads a noncollinear ferrielectric $δ$-phase energetically as stable as the ferroelectric $α$-phase. Its ferrielectricity is induced by the phonon frustration, i.e., the competition between ferroelectric and antiferroelectric modes, providing more routes to tune its polarity. Besides its prominent properties like large band gap, large polarization, and high Curie temperature, more interestingly, the morphotropic phase boundary between $α$- and $δ$-p…
Diffuse phase transition and electrical properties of lead-free piezoelectric (LixNa1-x)NbO3 (0.04 to x to 0.20) ceramics near morphotropic phase boundary
A correlation between the crystal structure and magnetic properties of system (1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase boundary was studied using X-ray and neutron diffraction, magnetometry, and Mossbauer spectroscopy measurements. Increase in the dopants content leads to the structural transition from the rhombohedral phase to the cubic phase via a formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic structure changes from the modulated G-type antiferromagnetic to the collinear antiferromagnetic via a stabilization of the non-collinear antif…
Interfaces formed by correlated oxides offer a critical avenue for discovering emergent phenomena and quantum states. However, the fabrication of oxide interfaces with variable crystallographic orientations and strain states integrated along a film plane is extremely challenge by conventional layer-by-layer stacking or self-assembling. Here, we report the creation of morphotropic grain boundaries (GBs) in laterally interconnected cobaltite homostructures. Single-crystalline substrates and suspended ultrathin freestanding membranes provide independent templates for coherent epitaxy and constrai…
Enhanced room-temperature electromechanical coupling in the lead-free ferroelectric system $(1-x)$BaZr$_{0.2}$Ti$_{0.8}$O$_{3}$ - $x$Ba$_{0.7}$Ca$_{0.3}$TiO$_{3}$ (abbreviated as BZCT) at $x=0.5$ is attributed to the existence of a morphotropic phase region (MPR) containing an intermediate orthorhombic ($O$) phase between terminal rhombohedral ($R$) BZT and tetragonal ($T$) BCT phases. However, there is ambiguity regarding the morphotropic phase transition in BZCT at room temperature - while some experiments suggest a single $O$ phase within the MPR, others indicate coexistence of three polar …
Spatially modulated morphotropic phase boundaries in a compressively strained multiferroic thin film
University of Southern California(南加州大学);University of Michigan, Dearborn(密歇根大学迪尔伯恩分校);University of California, Berkeley(加州大学伯克利分校);Cornell University(康奈尔大学)