Morphotropic Phase Boundary Systems Research Articles

Electric-field-induced phase transformation at a lead-free morphotropic phase boundary: Case study in a 93%(Bi0.5Na0.5)TiO3–7% BaTiO3 piezoelectric ceramic

The electric-field-induced strain in 93%(Bi0.5Na0.5)TiO3–7%BaTiO3 polycrystalline ceramic is shown to be the result of an electric-field-induced phase transformation from a pseudocubic to tetragonal symmetry. High-energy x-ray diffraction is used to illustrate the microstructural nature of the transformation. A combination of induced unit cell volumetric changes, domain texture, and anisotropic lattice strains are responsible for the observed macroscopic strain. This strain mechanism is not analogous to the high electric-field-induced strains observed in lead-based morphotropic phase boundary systems. Thus, systems which appear cubic under zero field should not be excluded from the search for lead-free piezoelectric compositions.

Bi(NiaX1-a)O3-PbTiO3계 압전 신조성(X-Ti,Nb)의 내전압 특성 향상

Lead-free ferroelectric ceramics are widely researched today for industrial applications as sensors, actuators and transducers. Since Pb(Zr a Ti 1-a )O₃(PZT) has high Curie temperature (TC), high piezoelectric properties near its morphotropic phase boundary (MPB) composition and small temperature dependence electrical behavior, it has been used to commercial materials for wide temperature range and different application fields. According to the tolerance factor concept, since the Bi 3+ cation with 12-fold coordinate has a smaller ionic radius than 12-fold coordinate Pb 2+ , most bismuth based perovskites possess a smaller tolerance factor. Therefore, MPBs with a higher TC may be expected in Bi(Me 3+ )O₃-PbTiO₃ solid solutions. As in lead based perovskite systems, it is clear that we need to explore more materials in simple or complex bismuth based MPB systems. The objective of this study is to investigate the Bi(Ni 1-a X a )O₃-PbTiO₃ (X=Ti 4+ , Nb 5+ ) perovskite solid-solution. For improving the electronic conduction problem, the magnesium and manganese modified system was also studied.

Morphotropic phase boundaries in(BiScO3)1−x(PbTiO3)x(0.60<x<0.75)and their relation to chemical composition and polar order

We have performed a structural study of the morphotropic phase boundary system $(1\ensuremath{-}x)\mathrm{Bi}\mathrm{Sc}{\mathrm{O}}_{3\ensuremath{-}x}\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ in which both $A$ and $B$ sites of the perovskite are randomly occupied. A ${M}_{A}$ monoclinic phase coexisting with a tetragonal phase has been evidenced for concentration $0.60<x<0.70$. No evidence of local cations ordering nor chemical inhomogeneity has been found. Taking into account data of Eitel et al. [Jpn. J. Appl. Phys., Part 1 40, 5999 (2001); Jpn. J. Appl. Phys. 41, 2099 (2002)] and our results, a global phase diagram has been drawn. This phase diagram reveals some similarities with that of lead zirconate titanate. The results are discussed in relation with previous works in morphotropic phase boundary systems.

Lead-free piezoelectric ceramics vs. PZT?

Investigations in the development of lead-free piezoelectric ceramics have recently claimed properties comparable to that of PZT-based materials. In this work, the dielectric and piezoelectric properties of the various systems were contrasted in relation to their respective Curie temperatures. Analogous to PZT, enhanced properties are noted for morphotropic phase boundary (MPB) compositions in the Na,BiTiO3–BaTiO3 and the ternary system with K,BiTiO3, but offer properties significantly lower than that of PZTs. The consequence of a ferroelectric to antiferroelectric transition well below T C further limits their usefulness. Though comparable with respect to T C, enhanced properties reported in the K,NaNbO3 family are the result of increased polarizability associated with the T orthor-tetragonal polymorphic phase transition being compositionally shifted downward and not from a MPB as widely reported. As expected, the properties are strongly temperature dependent unlike that observed for MPB systems.

Predicting the position of the morphotropic phase boundary in high temperature PbTiO3-Bi(B′B″)O3 based dielectric ceramics

Two previously unreported PbTiO3-Bi(B′B″)O3 type solid solution systems possessing a high dielectric transition Curie temperature (TC) at their morphotropic phase boundary (MPB) were investigated. Both Bi(B′B″)O3 type compounds, Bi(Mg1∕2Ti1∕2)O3 and Bi(Mg1∕2Zr1∕2)O3, possess a low tolerance factor and display extensive solid solubility with PbTiO3. Dielectric and structural properties of the MPB systems were measured. Using a relationship presented in this paper, which relates the tolerance factor and the position of the MPB in PbTiO3 based systems, the approximate compositional position of the MPB in these systems was accurately predicted prior to synthesis. It is proposed that this relationship can be used as a guide in the search for PbTiO3 based MPB systems.

New High Temperature Morphotropic Phase Boundary Piezoelectrics Based on Bi(Me)O3–PbTiO3 Ceramics

New morphotropic phase boundary (MPB) piezoelectrics, with ferroelectric phase transition (Tc) exceeding that of PbZrO3–PbTiO3 (PZT), were investigated. Based on a perovskite tolerance factor-Tc relationship, new high Tc MPB systems were projected in the Bi(Me)O3–PbTiO3 system, where Me is a relatively large B+3-site cation. For the (1-x)BiScO3–(x)PbTiO3 solid solution, a MPB was found at x-0.64 separating the rhombohedral and tetragonal phases, with correspondingly enhanced dielectric and piezoelectric properties. A transition temperature Tc of ∼ 450°C was determined with evidence of Tc's on the order of ≥ 600°C in the BiInO3 and BiYbO3 analogues, though issues of perovskite stability remain for the smaller tolerance end-member systems.

Ferroelectric ceramics of 2(Pb,Sr)Nb2O6:(K,Na)NbO3 tungsten bronze morphotropic phase boundary system

Systematic study of the chemistry-structure-property relation in α(Pb1-xSrx)Nb2O6:β(K1-yNayNbO3 oxide system has been carried out for α:β = 2:l and x = y. The experimental work is focused around compositions near the potential morphotropic phase boundary (MPB) that separates the ferroelectric orthorhombic (m2m) and ferroelectric pseudo-tetragonal phase (mm2). Ceramics of various compositions are prepared by solid state route and characterized for crystallographic phases and phase transitions using X-ray diffraction and thermal expansion measurements. Dielectric properties of these compositions as a function of temperature and frequency are studied. XRD analysis indicates the coexistence of pseudo-tetragonal and orthorhombic phases near x = 0.295. The dielectric permittivity reaches a maximum and phase transition temperature reaches a minimum near this composition.

Characteristics of relaxor-based piezoelectric single crystals for ultrasonic transducers

For ultrasonic transducers, piezoelectric ceramics offer a range of dielectric constants (K/spl sim/1000-5000), large piezoelectric coefficients (d/sub ij//spl sim/200-700 pC/N), and high electromechanical coupling (k/sub t//spl sime/50%, k/sub 33//spl sime/75%). For several decades, the material of choice has been polycrystalline ceramics based on the solid solution Pb(Zr/sub 1-x/B/sub 2x/)O/sub 3/ (PZT), compositionally engineered near the morphotropic phase boundary (MPB). The search for alternative MPB systems has led researchers to revisit relaxor-based materials with the general formula, Pb(B/sub 1/,B/sub 2/)O/sub 3/ (B/sub 1/:Zn/sup 2+/, Mg/sup 2+/, Sc/sup 3+/, Ni/sup 2+/..., B/sub 2/:Nb/sup 5+/ Ta/sup 5+/...). There are some claims of superior dielectric and piezoelectric performance compared to that of PZT materials. However, when the properties are examined relative to transition temperature (T/sub 3/), these differences are not significant. In the single crystal form, however, Relaxor-PT materials, represented by Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PZN-PT), Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PMN-PT) have been found to exhibit longitudinal coupling coefficients (k/sub 33/)>90%, thickness coupling (k/sub t/)>83%, dielectric constants ranging from 1000 to 5000 with low dielectric loss 2000 pC/N, the later promising for high energy density actuators. For single crystal piezoelectrics to become the next generation material of ultrasonic transducers, further investigation in crystal growth, device fabrication and testing are required.

Ferroelectric Properties of Tungsten Bronze Morphotropic Phase Bounary Systems

Tungsten bronze ferroelectrics which have a morphotropic phase boundary (MPB) can have a number of enhanced dielectric, piezoelectric, and electrooptic properties compared to more conventional ferroelectric materials. The structural and ferroelectric properties of several MPB bronze systems are presented, including data from sintered and hot‐pressed ceramics, epitaxial thin films, and bulk single crystals. Included among these are three systems which had not been previously identified as morphotropic. The potential advantages and limitations of these MPB systems are discussed, along with considerations of the appropriate growth methods for their possible utilization in optical, piezoelectric, or pyroelectric device applications.