Microstructural Observations in Barium Calcium Magnesium Niobate

Microstructural studies on (1 − x )Ba(Mg_1/3Nb_2/3)O₃– x Ca(Mg_1/3Nb_2/3)O₃ (BCMN) complex perovskite compounds, which are mixtures of Ba(Mg_1/3Nb_2/3)O₃ (BMN) and Ca(Mg_1/3Nb_2/3)O₃ (CMN), were conducted using scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. Pure BMN and CMN both have a 1:2 ordered structure, via the chemical ordering of B-site cations; however, the tilting of oxygen octahedra is involved in pure CMN, whose structure has a 1:2 ordered monoclinic unit cell that is characterized by (±1/6,±1/6,±1/6)-type superlattice reflections in electron diffraction patterns along the [110] zone axis that is based on a simple cubic perovskite. Studies of the morphologic differences have indicated two types of inhomogeneities in a mixture of the BCMN system: (i) a rather large-scale segregation (i.e., grain sizes of several micrometers), where the grains are separated compositionally as being barium-rich or calcium-rich, and (ii) fine-scale lamellar-type segregations 20 nm wide and 200 nm long. The segregation that is caused by Ba and Ca ions can be identified by the difference of superlattice modulations from high-resolution transmission electron microscopy lattice images.     

Interfacial Structure of Disordered-Ordered Domain Boundaries in Lanthanum-Doped Barium Magnesium Niobate

Microstructural studies on the interfacial boundaries of disordered and 1:2 ordered domains in lanthanum-doped (Ba_0.975La_0.025)(Mg_0.34Nb_0.66)O₃ were performed using high-resolution transmission electron microscopy and synchrotron powder X-ray diffractometry. Disordered and 1:2 ordered domains both coexisted in a single grain. Each domain occupied its own region, and the interfaces were atomically sharp and coherent. The wavelength of the superlattice modulation in the 1:2 ordered domain was ∼0.71 nm. The transition from the 1:2 ordered region to the disordered one could be differentiated at the interface by using the superlattice modulations in the 1:2 ordered domain. From these observations, a deducible interfacial model also was presented.     

Microstructural Characteristics of Strontium Magnesium Niobate

Microstructural studies were conducted on the domain boundaries in Sr(Mg_1/3Nb_2/3)O₃ (SMN) complex perovskite compound using X-ray diffractometry and transmission electron microscopy. Both the 1:2 chemical ordering of B-site cations and the tilting of oxygen octahedra were involved in SMN. SMN had a 1:2 ordered monoclinic unit cell, which was distorted by the antiphase tilting of oxygen octahedra. Two types of domain boundaries were found: the antiphase boundaries (APBs), which are not confined crystallographically, and the ferroelastic domain boundaries, which were parallel to the crystallographic planes. SMN had the superlattice reflections of type ±⅙[111] and ±½[111] in the electron diffraction patterns, which cannot be indexed in terms of the 1:2 ordered trigonal phase with only a hexagonal unit cell. The presence of the ferroelastic domains that contained both the 1:2 ordered and the antiphase tilting had been verified by a high-resolution transmission electron microscopy lattice image. The structure of SMN was well explained by a model proposed by other researchers. The formation of the 1:2 ordered domains preceded the ferroelastic domains. Normally, the growth of the ferroelastic domain is not affected by APBs, but it is interrupted by them when the driving force for growth is insufficient, resulting in the stoppage of the domains at APBs.     

Effect of Barium Titanate on Microstructural Evolution and Properties of Lead Zinc Magnesium Niobate Ceramics

BaTiO₃ (BT) addition vastly alters the dielectric behavior of lead zinc magnesium niobate (PZMN) relaxor ferroelectrics. Heat treatment, including the sintering process, influences the dielectric properties through changes in the distribution of heterogeneous compositions and in the extent of diffused phase transition. With more than 15 mol% BaTiO₃ addition, two cubic phases composed of Ba-rich and Ti-rich PZMN substances exist. The destruction of the BaTiO₃ phase and reconstruction of Ba-rich and Ti-rich regions are initiated during heat treatment, and the extent of destruction and reconstruction determines the dielectric properties of the PZMN ceramics. The BT-rich PZMN phase, which occurs with higher BaTiO₃ addition, plays a less important role in the present investigation.     

Infrared Spectroscopic Investigations in Ordered Barium Magnesium Niobate Ceramics

Highly ordered Ba(Mg_1/3Nb_2/3)O₃ ceramics from hydrothermal powders were investigated for the first time using infrared spectroscopy. The experimental data were analyzed in view of the 16 predicted modes of the trigonal structure and adjusted by a four–parameter semiquantum model. The obtained phonon parameters allowed us to calculate the real part of the dielectric permittivity and losses in all infrared regions, and also to estimate the quality factor ( Q ) for this material in the microwave region. The values obtained for the dielectric permittivity (ɛ'= 19) and Q (12 800 at 10 GHz) showed that hydrothermal Ba(Mg_1/3Nb_2/3)O₃ ceramics are good materials for passive components in microwave circuits.     

Dielectric and Structural Characteristics in Barium Lanthanum Magnesium Niobate

The dielectric properties and their related microstructural characteristics in solid solutions of (1 — x )Ba(Mg_1/3Nb_2/3)O₃ (BMN)— x La(Mg_2/3Nb_1/3)O₃ (LMN) (BLMN) were investigated by measuring the relative permittivity (ɛ_r), Q value, and temperature coefficient of resonator frequency (τ_f), and by observing the microstructure using transmission electron microscopy. The trend of variation of the temperature coefficient of the dielectric permittivity (τ_ɛ) was the same for our solid solutions as that reported by Reaney et al . When the tolerance factor ( t ) was >1.01 in BLMN with composition x = 0 to 1.0, where the tilting of oxygen octahedra was not involved, the components of the microstructure included a disordered and transition phase as well 1:1 and 1:2 ordered phases. In the region where 1.01 < t < 0.96 with x = 0.2 to 0.7, the 1:1 order, the disorder, and the phase due to the antiphase tilting of oxygen octahedra were present. Finally, in the region where t < 0.96 with x = 0.7 to 1.0, the microstructure of BLMN was the same as that of the pure LMN, including the 1:1 order and the antiphase, inphase tilting of oxygen octahedra, and the antiparallel shift of A-site cations.     

弛豫铁电陶瓷Ba(Mg,Nb)O_3的制备及性能研究

采用传统陶瓷烧结方法,在空气气氛下烧结制得Ba(Mg,Nb)O3(BMN)陶瓷,并分析了烧结温度对体系相组成及相结构的影响。X射线衍射(XRD)研究表明,随着烧结时间的增加,体系中钙钛矿相也相应增加。红外(FTIR)研究研究表明结构无序的BMN钙钛矿相中部分的区域出现了结构有序现象。通过X射线光电子能谱(XPS)可以发现,随着烧结温度的增加,体系中Nb2O5进入Ba(Mg1/3,Nb2/3)O3晶格。微波介电性能表明,随着烧结温度的增加,Ba(Mg,Nb)O3的rε和Qf值有逐渐增加的趋势。     

Interfacial Structure of Ordered Domains in Barium Lanthanum Magnesium Niobate

Microstructural studies on the interfacial boundaries of 1:1 and 1:2 ordered domains in (Ba_0.9La_0.1)(Mg_0.37Nb_0.63)O₃ were conducted using high-resolution transmission electron microscopy and X-ray diffractometry. Both 1:2 and 1:1 ordered domains coexisted in a fully ordered single grain. Each ordered domain occupied its own region, and the interfaces were atomically sharp and coherent. The wavelength of the superlattice modulation was ∼0.47 nm in the 1:1 ordered domain and ∼0.71 nm in the 1:2 ordered domain. The transition from the 1:2 ordered region to the 1:1 ordered region was clearly shown at the interface. These observations well support the structural models that have been previously presented.     

Microstructure and Dielectric Properties of Barium Strontium Magnesium Niobate

Dielectric properties and their related microstructural characteristics in solid solutions of (1 – x )Ba(Mg_1/3Nb_2/3)O₃– x Sr(Mg_1/3Nb_2/3)O₃ (BMN–SMN, or BSMN) were investigated by measuring the relative permittivity (ɛ_r), Q values, and temperature coefficient of resonator frequency (τ_f), and by observing microstructure using transmission electron microscopy. When the tolerance factor ( t ) was >0.99 in BSMN with composition 0 < x < 0.5, where the tilting of oxygen octahedra was not involved, the microstructure included only 1:2 ordered phase. In the region where 0.99 > t > 0.97 with 0.7 < x < 1.0, the phase due to the antiphase tilting of oxygen octahedral, the disordered phase, and the 1:2 ordered phase were also present. In a few of the grains, core–shell-type structures, whose main components were dislocations and stacking faults, were found in the solid solution of BSMN.     

Densification and Microstructural Development of the Reaction Sintering of Strontium Barium Niobate

SrNb₂O₆ and BaNb₂O₆ were selected as the precursor powders for the reaction sintering of strontium barium niobate of the composition Sr _x Ba_{1− x} Nb₂O₆ ( x = 0.5 and 0.6) (SBN). In comparing the densification behavior of the reaction sintering and the normal sintering of SBN, it was observed that the densification rate of the former was slower during reaction but became faster after reaction. It was also found that the chemical reaction occurred prior to densification, but a high-density and uniform microstructure could be obtained for the reaction-sintered sample. The densification rate of the reaction-sintered sample was pronouncedly enhanced when the reaction was almost completed. We also proposed the reason for the enhancement of the densification rate of the reaction-sintered sample when the reaction was almost completed. A high-density (>98% of the theoretical density), uniform, and fine-grained (3-4 µm) SBN microstructure could be achieved by using reaction sintering.     

High-Resolution Transmission Electron Microscopy Observations on Antiphase Boundaries in Barium Lanthanum Magnesium Niobate

Atomic structural observations on the antiphase boundaries (APBs) in the complex barium lanthanum magnesium niobate perovskite compound Ba_0.7La_0.3(Mg_0.43Nb_0.57)O₃ (BLMN), which has a 1:1 chemical ordering of B-site cations, were conducted using high-resolution transmission electron microscopy. Using APB contrast, the curved APB was determined to have a ledged structure, with a terrace that was composed of the (111) plane at an atomic level. In APBs with finite widths, microfacets on the (111) planes also were observed.     

Defect Structure and Phase Relations of Highly Lanthanum-Doped Barium Titanate

Incorporation of La³⁺ into the BaTiO₃ lattice was studied on samples of various composition, using quantitative WDS microanalysis (EPMA) in combination with scanning electron microscopy (SEM) and X-ray powder diffractometry (XRPD). Direct determination of solid-solution formulas by microanalysis supports the structure model of a solid solution with La³⁺ on Ba²⁺ sites and a deficient Ti⁴⁺ sublattice, independent of the starting composition. Solid solution extends on the tie line, which points from BaTiO₃ to La₄Ti₃O₁₂, to the composition of approximately Ba_0.70- La_0.38Ti_0.925( V "")_0.075O₃. On the basis of these results, the BaTiO₃-rich part of the BaO-La₂O₃-TiO₂ phase diagram was constructed.     

Characterization of Lanthanum-Doped Barium Titanate Ceramics Using Impedance Spectroscopy

The electrical properties of two single-phase, lanthanum-doped BaTiO₃ compositions, x = 0.03 and x = 0.20, in Ba_{1– x} La _x Ti_{1– x /4}O₃ were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C. Samples heated in oxygen were electrically insulating, whereas those heated in argon lost oxygen and were semiconducting at room temperature, irrespective of x . Samples heated in air showed intermediate electrical properties and also were electrically inhomogeneous; the two compositions showed different electrical behaviors, and a model for each, based on oxygen nonstoichiometry within the ceramics, is proposed. Oxygen deficiency in samples sintered in air was avoided by heating at 1200°C, instead of 1350°C. Alternatively, oxygen lost from ceramics heated in air at 1350°C was regained by postannealing in oxygen at 1350°C.     

Formation of Lead Magnesium Niobate Perovskite from Niobate Precursors Having Varying Magnesium Content

Formation of lead magnesium niobate (PMN) perovskite phase using a columbite type of precursor together with the addition of excess MgO has been investigated. When MgO and Nb₂O₅ are reacted with 1:1 stoichiometry, a minor amount (}2%) of Mg₄Nb₂O₉ is formed along with the columbite-type phase which in turn could lead to the formation of a minor amount of "free Nb₂O₅" in the precursor. This may be the reason for the formation of small amounts of pyrochlore phase during the synthesis of PMN perovskite from the stoichiometric 1:1 precursor. However, it has been found that the perovskite phase can easily be stabilized by the addition of a large excess of MgO in the precursor, although this leads to additional Mg-Nb-O phase Mg₄Nb₂O₉, besides the columbite-type phase MgNb₂O₆. It has been shown that, after this precursor reacts with PbO to form the PMN perovskite, the excess Mg present in the Mg-rich niobate precursor separates out as MgO, as evidenced by X-ray diffraction, which can be removed by leaching with dilute nitric acid, thus forming pure PMN.     

Mechanochemically Synthesized Lead Magnesium Niobate

Lead magnesium niobate (PMN) of high sintered density has been successfully prepared by a mechanochemical fabrication technique from mixed oxides of PbO, MgO, and Nb₂O₅. The novel technique skips the phase-forming calcination steps at intermediate temperatures that are almost always required in the most widely employed columbite method. The solid-state reactions among constituent oxides are activated by mechanical energy instead of calcination at elevated temperatures. Nanosized PMN particles of perovskite structure with a minimized degree of particle agglomeration were formed when the oxide mixture was mechanically activated for 20 h. The resulting PMN powder was sintered to a density of ∼99% theoretical density at 1050°C for 1 h. The sintered PMN exhibited a peak dielectric constant of 18 080 at a frequency of 100 Hz at -11°C.     

Microstructure Characterizations in Calcium Magnesium Niobate

Microstructural studies on the domain boundaries in Ca(Mg_1/3CNb_2/3)O₃ (CMN) complex perovskite compound were conducted using X-ray diffractometry and transmission electron microscopy. The 1:2 chemical ordering of B-site cations and the tilting of oxygen octahedra were involved in the CMN microstructure, as inferred from the presence of two types of domain boundaries. One type was the antiphase boundaries (APBs), which did not lie on a specific set of crystallographic planes. These boundaries were caused by the chemical 1:2 ordering of B-site cations, magnesium and niobium. The other type was the ferroelastic domain boundaries, which were parallel to a certain crystallographic plane. Therefore, CMN had the 1:2 ordered monoclinic unit cell distorted by the antiphase or in-phase tilting of oxygen octahedra. CMN had the mixed phases rather than the homogeneous phase.     

铌酸锶钡/钛酸锶钡复相陶瓷形成过程研究

应用粉末-溶胶工艺合成出铌酸锶钡/钛酸锶钡复相陶瓷(SBN/SBT)。采用X射线衍射技术研究了不同预烧温度的原始粉料、不同烧结温度和不同保温时间得到的铌酸锶钡/钛酸锶钡复相陶瓷。研究表明:钨青铜相和钙钛矿相共存于体系之中。复相陶瓷形成过程中形成了TiO2、BaNb2O6(BN)、SrNb2O6(SN)等中间相,增加烧结温度至1250℃,形成了铌酸锶钡/钛酸锶钡复相陶瓷。     

Low-Temperature Route to Lead Magnesium Niobate

Lead magnesium sniobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), was prepared by a sol-gel technique using alkoxide precursors. The hydrolysis-condensation mechanism leads to a translucent gel which is dried under hypercritical conditions to avoid collapse of the porous texture. After drying, the aerogel exhibits a B-deficient pyrochlore structure which progressively inserts magnesium oxide when the temperature increases. Near 700°C, this pyrochlore phase completely transforms into the PMN-perovskite phase. Above 1000°C, the loss of lead oxide leads to the destabilization of the PMN-perovskite with formation of an A-deficient pyrochlore phase.     

Cation Ordering and Dielectric Characteristics in Barium Zinc Niobate

Barium zinc niobate (Ba(Zn_1/3Nb_2/3)O₃) (BZN) complex perovskite has been reported to have special microwave dielectric properties with close relation of its ordered structure. This study investigated the effect of calcination on the evolution of ordered structure and on quality factor with Raman spectroscopy, X-ray diffractometry, and transmission electron microscopy. The results revealed that single calcination at a lower temperature inhibited the growth of the ordered domain during sintering. In contrast, the 1:2-ordered domain in double-calcined BZN powder grew significantly with a higher sintering temperature and a longer soaking time. It is attributed that double calcination caused a higher degree of 1:2 ordering and better homogeneity. At the same time, the quality factor of the sintered ceramic body was highly promoted when using double-calcined powder. A close relation of the quality factor with the size of ordered domain, the degree of 1:2 ordering, and the relative density of BZN ceramics was presented.     

Diffuse Phase Transition of Tantalum-Bearing Strontium Barium Niobate

The dielectric constants, ε' and ε", of tantalum-bearing strontium barium niobate (SBNT) ceramics were measured as functions of temperature and frequency. The phase transition of SBNT became ambiguous by adding Ta and the apparent Curie temperature determined from the maximum of ε' had a linear relation with the axial ratio c/a. A dielectric loss peak was observed in the phase transition region of SBNT, and its peak frequency increased with temperature. The loss peak was attributed to dielectric relaxation by the jump between two states with different polarizing directions as a preliminary phenomenon of the phase transition. A model based on the local variation from one unit cell to the next rather than the macroscopic compositional fluctuation in the crystal was proposed for the mechanism of diffuse phase transition.