Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

The process and nature of structural ordering and the factors that influence them have been investigated in the microwave dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy. The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

Perovskite formation and dielectric responses in Pb(Zn1/3Nb2/3)O3-modified Pb(Zn1/3Ta2/3)O3-PbTiO3 ceramics

Pb(Zn_1/3Ta_2/3)O₃-PbTiO₃ ceramic compositions were modified by the introduction of Nb to the octahedral lattice sites. Resultant tendencies in the perovskite formation and dielectric properties were examined. System powders were prepared using a B-site precursor method. Developed structures and lattice parameters of the system compositions were investigated by powder X-ray diffractometry, from which the parameter of a hypothetical perovskite Pb(Zn_1/3Ta_2/3)O₃ is proposed. Weak-field low-frequency dielectric responses of the system ceramics were measured.     

Dielectric properties of Pb(Zn1/3, Nb2/3)O3 ceramics modified by Ba(Zn1/3, Nb2/3)O3 and BaTiO3

Dielectric properties of lead zinc niobate (PZN) ceramics modified by barium zinc niobate (BZN) and BaTiO₃ (BT) were investigated. By adding the modifier of BT and BZN, the stabilization of perovskite phase of PZN increased, but its Curie temperature decreased linearly with the amount of added modifier. Room temperature dielectric constant of PZN increased by addition of stabilizers up to 12 and 15 mol% of BZN and BT, respectively. The maximum room temperature dielectric constant was observed to be 7800 at 12 mol% of BZN, and 9800 at 15 mol% of BT, respectively.     

Stabilization of the perovskite phase in Pb(Zn1/3, Nb2/3)O3 ceramics modified by Ba(Zn1/3, Nb2/3)O3 and BaTiO3

Stabilization of the perovskite phase in PZN-BT-BZN ceramics prepared by solid-state sintering was investigated. With the addition of BT and/or BZN, the amounts of perovskite phase in PZN ceramics increased, but the amount of pyrochlore phase decreased. Optimum calcination conditions for this system, to obtain PZN ceramics with the minimum amount of the pyrochlore phase, are a temperature range between 950 and 1000°C and a sintering time of 2–4 h. The perovskite phase of these systems could be 100% stabilized by the addition of more than 7 mol% BT, 8 and 10 mol% BTZN and BZN, respectively. This revised version was published online in November 2006 with corrections to the Cover Date.     

Pb(Zn1/3Nb2/3)O3-Ba(Zn1/3Nb2/3)O3铁电陶瓷结构与性能的研究

采用固相反应的方法系统地研究了BZN稳定PZN基陶瓷的相结构与介电性能.随着BZN含量的增加,PZN-BZN陶瓷中钙钛矿相的稳定性增强,居里温度近似呈线性下降,室温介电常数和介质损耗随也显著降低,最小值分别为380和0.002.为获得100%钙钛矿结构的PZN基陶瓷所需BZN的最小用量为8mol%～10mol%,当BZN的mol%超过15mol%时,PZN基陶瓷中钙钛矿相所占的百分比不再受烧结工艺的影响,基本保持100%.1kHz时Pb0.9Ba0.1Zn1/3Nb2/3O3陶瓷的最大介电常数Kmax=8680,tgδ=0.02,相应的居里温度Tm为24℃.     

Effects of non-stoichiometry and chemical inhomogeneity on the order-disorder phase formation in the complex perovskite compounds,Ba(Ni1/3Nb2/3)O3and Ba(Zn1/3Nb2/3)O3

The order-disorder phase formation of the complex perovskite compounds, Ba(Ni_1/3Nb_2/3)O₃ and Ba(Zn_1/3Nb_2/3)O₃, was investigated by various heat treatments. Heat-treated samples were characterized using X-ray diffraction, SEM, and EDS, interactively. On the basis of lattice parameter measurements, the defect concentration in the complex perovskite compounds was thought to control ordered or disordered phase formation. The chemical inhomogeneity in the calcined powder was responsible for the formation of a liquid phase in the non-equilibrium state. These compounds are postulated to melt incongruently above temperature at which the ordered phase forms. Irrespective of extended heat treatments, second phases were observed but could not be identified by XRD due to lack of information. The second phase in BNN was unreacted NiO with a small amount of barium and niobium, and the second phase in BZN was a pyrochlore-like compound of which the composition was BaNb = 11 with a small amount of zinc.     

Ferroelectricity of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics in the vicinity of morphotropic phase boundary

The morphotropic phase boundary (MPB) in the (0.85 – x)Pb(Zn_1/3Nb_2/3)O₃ – 0.15BaTiO₃ – xPbTiO₃(0 < x < 0.2) ceramic system was delineated by x-ray diffraction analysis. Polarization hysteresis loop measurements at room temperature were performed for compositions in the vicinity of the MPB. Experimental results demonstrate that the MPB, by its definition the rhombohedral and tetragonal phase coexist in the present system, is a broad composition region where the value of x ranges from 0.12 to 0.18. The remanent polarization, P _r, increases with PbTiO₃(PT) reaching a maximum value of 18 C/cm² at 15 mol%PT, then decreases remarkably with further PT addition, whereas the variation of coercive field, E _c, with PT content shows the opposite trend. The effect of PT incorporation on P _r is more pronounced than on E _c. Correlation between the degree of lattice distortion, instead of the maximization of the polarization orientations inherent to both phases, and P _r is attained to account for the observed phenomenon. The dependence of E _c upon PT content, however, reflects the transition from typical relaxor ferroelectrics to weak normal ferroelectrics, as confirmed by the results of the dielectric measurement.     

A new type of ordering in Ba(Zn1/3 Ta2/3)O3 ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

The substitution-site of Cd2+ in Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Dielectric and ferroelectric properties of Bi(Zn1/2Ti1/2)O3-PbTiO3-PbZrO3 ternary ceramics

Ceramics of a new ternary solid solution system, xBi(Zn(1/2)Ti(1/2))O(3-yPbTiO(3)z)PbZrO(3) (xBZT-yPT-zPZ), with compositions along the solubility limit curve are prepared by solid-state reaction and sintering technique. Two morphotropic phase boundaries (MPBs) separating the orthorhombic and tetragonal (MPB(O-T)) phases and the tetragonal and rhombohedral (MPB(T-R)) phases, respectively, are observed with increasing z (0.10 ≤ x ≤ 0.21; 0 ≤ y ≤ 0.49). It is found that the transition from the ferroelectric to paraelectric phase becomes more diffuse with the addition of BZT into the PZT solid solution. Enhanced dielectric and ferroelectric properties appear at MPB(R-T), which exists over a wide composition region (0.45 ≤ z ≤ 0.6), as revealed by X-ray diffraction and dielectric measurements. The dielectric constant reaches a maximum value (ε' = 1250) on the tetragonal majority side of the MPB. The highest remnant polarization (P(r) = 34.2 μC/cm(2)) is found in the composition at the center of the MPB, where the rhombohedral and tetragonal phases coexist in almost equal quantities.     

Crystal structure and microwave dielectric properties of Ba[(Zn1-xMgx)1/3Nb2/3]O3 ceramics

Journal of Materials Science: Materials in Electronics - Ba[(Zn1-xMgx)1/3Nb2/3]O3(x?=?0?~?0.9) ceramics were prepared by the traditional solid-phase reaction sintering...     

Pb(Ni1/3Nb2/3)O3-PbTiO3系统准同型相界附近的介电异常

用两步合成法制备了(1-x)Pb(Ni1/3Nb2/3)O3-xPbTiO3(x=0.300.40)陶瓷,对其相结构和介电性能进行了研究. XRD分析表明,准同型相界在PT含量x=0.340.38范围内. 介电性能研究结果表明,组成在准同型相界处的试样, 其介电常数呈现最大值.同时还发现,准同型相界处的陶瓷出现介电双峰,其中一个为弛豫型?铁电相向顺电相转变的相变峰;另一个介电峰处于130150C的高温区, 可能是由镍离子变价、相结构变化等缺陷引起的松弛极化产生的.