Papers by Keyword: Morphotropic Phase Boundary

Abstract: In this study, (1-x)Pb_0.92La_0.08(Zr_0.4Ti_0.6)O₃ - xPb (Zn_1/3Nb_2/3)O₃ (PLZT-PZN, x = 0, 0.05, 0.10, 0.15 0.20 and 0.25) ceramics with pure perovskite were synthesized by mixed oxide synthetic route via a rapid vibro-milling technique. The ceramic pellets were sintered at 1250°C for 4 h. The phase formation and composition was investigated using X-ray diffraction. The dielectric properties of the densified samples were investigated by LCR meter as a function of temperature and frequency. It can be seen that when optimal amount of PZN was added to tetragonal Pb_0.92La_0.08(Zr_0.4Ti_0.6)O₃ ceramics, the electrical properties were found to be optimal.

Abstract: In this study, the (Mn, Sb) co-tuned PbCa_0.01[(Mn_xZn_0.1-x)_1/3(Sb_xNb_0.1-x)_2/3 (Zr_0.505Ti_0.4895)_0.9]O₃ (PCZMNSZT-100x) ceramics were prepared near the morphotropic phase boundary (MPB) using the wolframite precursor method. The phase structure evolutions, electrical and temperature stability properties were systematically investigated. As the fraction of rhombohedral phase increases, the degree of disorder in the diffused phase transition (DPT) correspondingly increased and the “hard” piezoelectric characterization would be enhanced. Moreover, the temperature change rate of k, Q_m and f_r can be tuned by adjusting the x content. The specimens with x=0.08 exhibit the obtained values as k_p ~ 0.50, k_t ~ 0.52, Q_m ~ 1550, and the low temperature change rate of properties having Δf_r/f_r = -0.02% and ΔQ_m/Q_m = 10.5%, up to 100 °C. To evaluate the material feasibility, the proposed multi-bulk step-down transformers using a ring/dot structure are fabricated. Their obtained electrical properties have a maximum efficiency of 92% with an output power of 15 W, a voltage gain of 0.68 and a nearly zero temperature change rate of resonant frequency are found at the load of 100 Ω.

Abstract: Doping effect on the lattice parameters, vibration modes, dielectric and piezoelectric properties of LiSbO₃, LiTaO₃ and LiNbO₃ substituted lead-free K_0.5Na_0.5NbO₃ (KNN) ceramics are investigated. All compositions are crystallized in morphotropic phase boundary region. Enhanced piezoelectric and electromechanical response d₃₃ ~176–197 pC/N, k_p ~45%–48%, and k_t ~34%–47% obtained in the doped ceramics are due to the presence of the polymorphic phase transition between orthorhombic and tetragonal phase at room temperature.

Abstract: The phase structure, microstructure and electrical properties of (1-x)Pb (Zr_y Ti_1-y)O₃-xSm(Fe³⁺_0.5, Nb⁵⁺_0.5)O₃ (PZT–SFN) (with x = 2 %, 41%≤ y ≤57 %) piezoelectric ceramics were prepared by the conventional solid state method, and effects of SFN and the Zr/Ti ratio content on the piezoelectric properties of PZT ceramics were mainly investigated. A stable solid solution has been formed between PZT and SFN, and a morphotropic phase boundary of PZT–SFN ceramics is identified in the range of 51% ≤ y ≤55 %. The Curie temperature of PZT–SFN ceramics decreases with increasing at Zr/Ti ratio content. A higher ε_r value and a lower tanδ value are demonstrated for the PZT–SFN ceramics with y = 53 %. The PZT–SFN ceramics with y = 53 % has an enhanced electrical behavior of k_p ~ 61.2 %, Q_m ~ 104, ε_r ~ 566, tanδ ~ 2.02 % and T_C ~ 370 ^OC. As a result, PZT–SFN ceramics are promising candidate materials for the field of lead piezoelectric materials and piezoelectric device.

Abstract: Lead-based piezoelectric ceramics have excellent piezoelectric properties with the compositions near the rhombohedral-tetragonal morphotropic phase boundary (MPB)^[1,2]. In these materials, the dielectric and piezoelectric properties show the maximal values at MPB. For lead-free piezoelectric ceramics, finding the MPB area is a promising way to improve their properties. In this paper, the (1-x-y)BaZrO₃-x(K_0.45Na_0.5Li0.05)NbO₃-yBi (Mg_0.5Ti_0.5)O₃ lead-free piezoelectric ceramics were prepared by solid-state reaction method, and their piezoelectric properties and dielectric properties were investigated. With the increase of KNLN content, the crystal structure changed from rombohedral phase to tetragonal phase, thus existed a MPB^[3,4] between rombohedral and tetragonal phase. At room temperature, the specimen with the composition at MPB (x=0.93, y=0.01) shows the optimal piezoelectric properties (d₃₃=225pC/N and k_p=45%), which indicates that this material is a potential lead-free piezoceramic.

Abstract: Anelastic and dielectric relaxation measurements have been carried out on poled and unpoled samples of the ferroelectric perovskite (Na_0.5Bi_0.5)_1−xBa_xTiO₃ (NBT-xBT), with composition in the range between pure NBT and the morphotropic phase boundary, 0 ≤ x ≤ 0.08. The complex elastic compliance spectra contain clear indications of both the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the phase diagram, which is difficult to obtain by diffraction techniques due to the very low distortions in both the tetragonal and rhombohedral phases and to the structural disorder in the Na/Bi sublattice. An extensive study is made for concentrations in the region of the morphotropic boundary (x ∼ 0.06) in order to find possible signatures of monoclinic phase, as for the case of PbZr_1-xTi_xO₃ (PZT). The main features in the anelastic curves are compared with those in the dielectric spectra and are tentatively related to different modes of octahedral rotations and polar cation shifts.

Abstract: Anelastic and dielectric spectroscopy measurements are presented, which, together with previous measurements [1], clarify some controversial aspects of the phase diagram of PbZr_1xTi_xO₃ close to the border with the antiferroelectric (AFE) phase, and at the morphotropic phase boundary (MPB). No evidence is found of a border separating monoclinic (M) from rhombohedral (R) phases, supporting recent structural studies according to which the two phases coexist, with the fraction of M prevailing near the MPB. A large frequency independent softening at the MPB indicates a genuine M phase over only finely twinned R phase. A new phase transition is found in both the anelastic and dielectric spectra at x = 0.1, at a temperature T_IT between the Curie temperature T_C and the boundary T_T to the phases with tilted octahedra. Such a diffuse transition is interpreted as onset of disordered tilts, which finally become ordered below T_T. In this manner, the phase diagram of PZT is rationalised with respect to the common tendency of perovskites to undergo tilting when the mismatch between the cation sizes exceeds a threshold.

Abstract: The mixed-oxide system Ba (Ti_1-xZr_x)O₃ (BTZ) with the simple perovskite structure was reported to exhibit the remarkable dielectric response around x = 0.08. In order to understand the origin of the response, we have investigated the crystallographic features of ferroelectric states in BTZ with 0 ≤ x ≤ 0.15 mainly by transmission electron microscopy. According to the constructed phase diagram of BTZ, when the Zr content increases from x = 0 around 300 K, the ferroelectric tetragonal state in BaTiO₃ is changed into the ferroelectric orthorhombic state around x = 0.03, and then into the ferroelectric monoclinic state around x = 0.06. That is, the monoclinic state with a polarization vector in the {110}_PC planes is present in BTZ with 0.07 ≤ x ≤ 0.15, where the subscript PC denotes the paraelectric cubic state. The notable feature of the monoclinic state is that it exhibits the herringbone-type domain structure consisting of nanometer-sized ferroelectric domains. It is thus understood that the remarkable dielectric response in BTZ should be associated with the presence of nanometer-sized domains with the monoclinic symmetry.

Abstract: The perovskite (Na_1/2Bi_1/2)TiO₃ (NBT) undergoes a series of structural and polar transitions starting from the high temperature paraelectric phase: tetragonal paraelectric, tetragonal antiferroelectric, rhombohedral antiferroelectric and finally rhombohedral ferroelectric, according to neutron diffraction and dielectric spectroscopy. In solid solution with BaTiO₃ (BT) the ferroelectric phase changes from rhombohedral to tetragonal, at the so-called morphotropic phase boundary, and the phases at higher temperature become ill-defined, also because of the large lattice disorder induced by the coexistence of differently charged cations in the same sublattice. Combined dielectric and anelastic spectroscopy measurements are presented, which clarify some issues related to the phase transitions in NBT-BT. The influence of Ba substitution on the tetragonal antiferroelectric phase is determined for the first time, and the possibility that a monoclinic phase, although with very short coherence length, exists near the morphotropic phase boundary is discussed in view of a large maximum of the elastic compliance.

Abstract: The effect of sintering temperatures (1050-1200 °C) on the phase formation, microstructure and dielectric properties of a binary system lead-free ceramic bismuth sodium titanate–bismuth potassium titanate were investigated. 0.8Bi_0.5Na_0.5TiO₃-0.2Bi_0.5K_0.5TiO₃; BNKT ceramics were successfully fabricated using the combustion technique. XRD results showed the rhombohedral-tetragonal morphotropic phase boundary (MPB). The SEM results showed the average grain size (0.51-2.59 µm) of the samples increased with the increase of sintering temperatures. The sample sintered at the optimum temperature of 1150 °C exhibited the maximum density, shrinkage, dielectric constant at Curie temperature and remanent polarization (P_r) which were around 5.65 g/cm³, 17.75%, 5014 and 1.6 mC/cm², respectively. The dielectric constant was related to the XRD results and density of the sintered ceramic.