Relaxor-like behavior of bismuth-based pyrochlores containing Sn

Dielectric relaxation studies have been made in pyrochlore (Bi_1.5Zn_0.5)(Zn_0.5?x/3Sn _x Nb_1.5?2x/3)O₇ ceramics where 0?≤?x?≤?1.5. The measurements of dielectric constant (?) and dielectric loss (tanδ) are made in the frequency range from 1 to 1,000 kHz at low temperatures from 100 to 450K. Frequency dispersion associated with dielectric relaxation phenomena in polycrystalline cubic pyrochlore is analyzed. The effect of Sn on the dielectric relaxation behavior and the physical mechanism giving polarization is briefly discussed.     

Studies on dielectric relaxation and high temperature conductivity of Bi1.5Zn1−x Nb1.5O7−x ceramics

The dielectric properties of cubic pyrochlore Bi_1.5Zn_1?x Nb_1.5O_7?x (BZN) ceramics with high dielectric constant, low dissipation factor are strongly affected by their lattice defects. The dielectric properties of BZN sintered in various atmosphere including ambient, N2, and O2 are investigated. The equilibrium high temperature conductivity was examined.     

Study of structure and dielectrc properties of non-stoichiometric Bi2O3-ZnO-Nb2O5 ceramics

Bi-based ceramics with pyrochlore structure exhibit interesting dielectric properties such as high dielectric constant and small dielectric loss at high frequency and low firing temperature. Structure and dielectric properties of non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x (with x?=??0.25～0.6) were investigated. The compounds departured from stoichiomeric compositions lead to structural parameters change. The second phase appeared when x?≥?0.4. The lattice parameters of cubic pyrochlore Bi_1.5?x ZnNb_1.5O₇ and grain size decreased as x increased. The experimental results show that dielectric constant decrease with increasing of the x value. The dielectric relaxation and defect resulting from non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x were discussed.     

Investigation of the physical properties of Bi1.5-xCdxZn0.92Nb1.5O6.92-x/2 pyrochlore ceramics

For the purpose of dielectric parameters tuning Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN) pyrochlore ceramics were subject to cadmium doping in accordance to the chemical formula; Bi_1.5-xCd_xZn_0.92Nb_1.5O_6.92-x/2 for 0.10 ≤ x ≤ 0.50. The main physical properties of the doped samples were investigated by means of X-ray diffraction, scanning electron microscopy associated with energy dispersion spectroscopy, temperature dependent dielectric constant and temperature dependent electrical resistivity to obtain the crystalline structure, the lattice parameter, the relative density, the surface morphology and chemical composition. Optimization of single phase Cd doped samples were possible for x?≤?0.14, beyond this limit, ZnO and Zn₃Nb₂O₈ minor phases grow through the structure of the BZN. For samples which exhibit single BZN phase, the dielectric constant, the electrical resistivity and the resistivity activation energy increased with increasing Cd content. The maximum obtainable dielectric constant as 259 and 224 with high signal quality factor of 690 and 1090 at 25 and 200 °C, respectively, was for the sample doped with 0.14 Cd. These values are promising for implantation of BZN in RF and microwave technology as a resonator with high quality signal.     

Raman Scattering Study of the Pb(Hf x Ti1−x )O3 Ceramics

Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(Hf_xTi_1–x)O₃ (PHT) (0.10 x 0.50) samples at room temperature and at 20 K. For x 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm^–1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the mass effect (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti⁴⁺ and Zr⁴⁺ and between Ti⁴⁺ and Hf⁴⁺ ionic radii. The behaviour of the mode at around 280 cm^–1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.     

Phase Decomposition and Dielectric Properties of Reactively Sputtered Bismuth Zinc Niobate Pyrochlore Thin Films Deposited from Monoclinic Zirconolite Target

Thin films of Bi₂O₃-ZnO-Nb₂O₅ system with cubic pyrochlore structure can be deposited using both cubic and monoclinic (zirconolite) targets. When monoclinic target was used, the as-deposited phase was nonequilibrium cubic monophase. After post-annealing in the 600–800^C range, phase decomposition occurred, resulting in more thermodynamically stable cubic pyrochlore and monoclinic zirconolite phases. The dielectric properties, such as dielectric constant and electric field dependent tunability, showed a steep increase along with phase separation. However, dielectric loss had a reverse tendency. The maximum tunability was about 38%, which exceeds that of cubic pyrochlore monophase films deposited from cubic target.     

Doping Mechanism and Permittivity Correlations in Nd-Doped BaTiO3

BaTiO₃ forms an extensive range of solid solutions with Nd₂O₃ by means of the double substitution mechanism: Ba + Ti 2Nd, as shown by both a phase diagram study and Rietveld refinement using powder neutron diffraction data. The solid solutions have the general formula Ba_1-xTi_1-xNd_2xO₃Odxd0.12 at 1300°C and 1300°C and O dxd at 1400°C. With increasing x, the symmetry changes from tetragonal to cubic at x 0.09. The sharp permittivity maximum at 127°C in stoichiometric BaTiO₃ broadens very rapidly with increasing x and gradually moves to lower temperatures: this appears to be because, with substitution of Nd onto Ti sites, formation of the ferroelectric domains is increasingly difficult because of the presence of dipole-inactive Nd³⁺ ions on the Ti sites.     

Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

Characteristics of Textured Ce-Zr Mixed-Oxide Films as Buffer Layer for YBCO Coated Conductors

Single- and multi-layer (Ce_{1 – x} Zr _x )O₂ films (0 x 0.84) on Si (100) and polycrystalline Ni substrates were prepared using RF and DC magnetron co-sputtering. XRD of scan analysis showed that all (Ce_{1 – x} Zr _x )O₂ films were biaxially oriented with the c-axis perpendicular to the plane of the film. During sputtering, DC power to the Zr target was fixed at 200 W, while RF power to the Ce target was set at 30 W, 50 W, or 100 W. As-deposited ZrO₂ film was amorphous and was crystallized by post-annealing. However, as-deposited (Ce_{1 – x} Zr _x )O₂ films were crystalline even when grown at room temperature and the structures of films were cubic or tetragonal depending on the Ce ion incorporation. It was found that multilayered CeO₂/(Ce_{1 – x} Zr _x )O₂/CeO₂ films could be deposited with a continuous compositional gradient in a sputtering batch. This layered CeO₂/CZO/CeO₂ structure can maintain its original texture after 800°C annealing and is therefore suitable for subsequent YBCO film growth. Furthermore, Ni diffusion is effectively blocked by the buffer layers just like the YSZ currently used in coated conductor fabrication.     

Structure and microwave dielectric properties of Sm(2−x)/3Li x TiO3

The structural evolution, and microwave dielectric properties of ceramics (x = 0.0 ≤ x ≤ 0.5) were investigated in this work. X-ray diffraction (XRD) results show that samples with x > 0.3 exhibit a single perovskite phase. Impurity phases of Sm₂Ti₂O₇ and TiO₂ appear and their amount increases with the decrease of x when x ≤ 0.3. TEM observation indicates that the A-site is ordered in x = 0.5, but not in x = 0.3). The dielectric constant decreases with the increase of x for 0.1 ≤ x ≤ 0.4 and then increases with further increase in x up to x = 0.5. The Q×f value decreases with the decrease of x due to the increased occurrence of Sm₂T₂O₇ secondary phase, defects and twinning boundaries. The temperature coefficient of resonant frequency is negative and its absolute value decreases greatly with the decrease of x value.     

Relaxor Behavior of (Sr0.8Ba0.2)TiO3 Ceramic Solid Solution Doped with Bismuth

The dielectric properties of (Sr_0.8Ba_0.2)_1-1.5xBi_xTiO₃ ceramics in the range 0 x 0.18 are investigated. A ferroelectric relaxor behavior is observed. The degree of the diffuseness and the relaxation of the phase transition increases as the Bi content increases. A random electric field is suggested to be responsible for the relaxor behavior observations. The dependence of the diffuseness on the grain size is presented.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Protonic Conduction in SrY0.5Ta0.5O3-Based Ceramics at Elevated Temperatures

The perovskite-type-oxide solid solution SrY_0.5+x Ta_0.5+x O_3– was synthesized and its properties were investigated. The single phase character of the samples was confirmed by X-ray diffraction when 0 x 0.02, while lines from the impurity phase SrY₂O₄ appeared in patterns of x 0.03. The conductivities of SrY_0.52Ta_0.48O_3– were about an order of magnitude higher than those of SrY_0.50Ta_0.50O₃. The results of electrochemical measurements such as emf measurements of gas concentration cells, isotope effect in conductivity, and oxygen partial pressure dependence of conductivity showed that SrY_0.52Ta_0.48O_3– exhibited pure protonic conduction in reducing atmospheres and p-type electronic conduction under high oxygen partial pressure conditions.     

Interaction between Water and Ceria-Zirconia-Yttria Solid Solutions

We have investigated the water solubility, oxygen isotope diffusivity, and oxygen surface exchange coefficient in a humid atmosphere of the system {(CeO₂)_x(ZrO₂)_1–x}_0.8(YO_1.5)_0.2 (x = 0–1) by using isotope exchange and secondary ion mass spectrometry (SIMS). The deuterium ion (²D^–) was detected from the {(CeO₂)_x(ZrO₂)_1–x}_0.8(YO_1.5)_0.2 polycrystals which were annealed in D₂O containing atmosphere. The solubility of deuterium in the polycrystals increased with the cerium content (x). The oxygen exchange rate constant () in air at T = 973 K shows a maximum at x = 0.2–0.3, which can be correlated to the compositional dependence of electronic conductivity of {(CeO₂)_x(ZrO₂)_1–x}_0.8(YO_1.5)_0.2. The effect of water on the surface exchange rate constant was more significantly observed for the samples with higher content of cerium x > 0.6.     

Dielectric Behavior and Magnetoelectric Effect in Ni0.75Co0.25Fe2O4 + Ba0.8Pb0.2TiO3 ME Composites

Magnetoelectric composites with ferrite + ferroelectric compositions xBa_0.8Pb_0.2TiO₃ + (1 – x) Ni_0.75Co_0.25Fe₂O₄ in which x varies as 0, 0.55, 0.70, 0.85 and 1.0 were prepared by ceramic method. X-ray analysis confirms single-phase formation in x = 0 and x = 1 compositions, whereas the presence of both phases is shown in x = 0.55, 0.70 and 0.85 compositions. Variation of dielectric constant () with temperature and frequency has been studied. All the samples have show linear magnetoelectric conversion in the presence of static magnetic field. Static magnetoelectric conversion factor, (dE/dH), was measured as a function of magnetic field in the samples with x = 0.55, 0.70 and 0.85 compositions. The maximum value of dE/dH was found to be 140 V/cm/Oe for x = 0.85 composition.     

Structures and Dielectric Properties of La-Substituted SrBi8Ti7O27 Ceramics

SrBi₈Ti₇O₂₇ ferroelectric ceramics with mixed Aurivillius structure were modified by La-substitution for Bi, and the dielectric properties were investigated together with the microstructure characterization. Solid solution of Sr(Bi_{1 – x} La _x )₈Ti₇O₂₇ was formed in the present ceramics for x 0.1, and (Bi,La)₄Ti₃O₁₂ secondary phase appeared at x = 0.15. For x 0.25, another phase Sr(Bi,La)₄Ti₄O₁₅ appeared, and (Bi,La)₄Ti₃O₁₂ disappeared gradually with increasing x, and vanished entirely at x = 0.35. With increasing x, both the dielectric constant and dielectric loss of the present ceramics increased firstly and reached their maximums 291 and 0.023 at 1 MHz, then decreased after x > 0.25. The temperature stable high- dielectric ceramics with low dielectric loss were created at the composition x = 0.5: = 122, tan = 0.0003 and = –619 ppm/°C at 1 MHz.     

Orientation Control of ZnO Thin Film Prepared by CVD

A series of materials represented by the formula Ni_1;Mo_1–/3O₄, where -1/5 1/3, were prepared by calcination of layered ammonium nickel molybdates having a general formula (NH₄)H_2xNi_3-xO(OH)(MoO₄)₂, where 0 x 3/2. Phase determination using high temperature X-ray diffraction studies showed that the variable stoichiometry of the precursor phase that allowed for Ni/Mo ratios between 0.75 and 1.5 led to the formation of a single phase of the form Ni_1;Mo_1–/3O₄ following calcination. AC impedance spectroscopy was used to investigate the electronic conductivity of the materials. The defect chemistry of these ternary ionic materials was modeled to correlate the electronic conductivity with the structure.     

Structural evolution and microwave dielectric properties of (1 − x)BaZn1/3Nb2/3O3 + xBaMg1/2W1/2O3 ceramics

Structural evolution and microwave dielectric properties of (1 − x)BaZn_1/3Nb_2/3O₃ + xBaMg_1/2W_1/2O₃ (0 ≤ x ≤ 1) system have been investigated in this work. All samples exhibit single perovskite phase except for the samples with x = 0 and x ≥ 0.8 in which barium niobate and BaWO₄ second phase existed, respectively. 1:1 cations ordering existed in the samples with x ≥ 0.1, and the ordering degree increases with the increase of x. Liquid phase sintering was observed in the sample with x ≥ 0.8. Dielectric constant decreases almost linearly from 40.8 to 17.4 with increasing x. Q × f value monotonically increases from 26,162 GHz to 64,705 GHz with increasing x. The τ_f value changes from +30 ppm/°C to −27.8ppm/°C. Near zero τ_f value of −1.4 ppm/°C could be obtained at x = 0.4 composition.     

Effect of Rare Earth Europium Substitution on the Microstructure,Dielectric, Ferroelectric and Pyroelectric Properties of PZT Ceramics

Polycrystalline samples of Europium modified lead Zirconate titanate (Pb_{1 – x} Eu_x)(Zr_0.55Ti_0.45)_{(1 – x/4)}O₃ with x = 0.00, 0.02, 0.04, 0.06 has been prepared by mixed oxide (MO) method at sintering temperature of 1250C. The structural characterization of the samples investigated by X-ray diffraction technique exhibit tetragonal structure. PEZT (2/55/45) ceramics show single perovskite phase. Scanning electron micrographs depict uniform, densely packed structure. Dielectric, Pyroelectric and Ferroelectric studies have been performed and are reported and discussed in this paper. PEZT (2/55/45) show good current responsivity (F_i), voltage responsivity (F_v) and detectivity (F_d), in comparison to other compositions under study. Moreover its ferroelectric properties (high remanent polarization with low coercive field) make it suitable material for nonvolatile memory applications.     

Sintering and dielectric properties of Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics via high-energy milling technology

The dense Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics is synthesized by high-energy milling technology from the coarse Bi_1.5ZnNb_1.5O₇ cubic pyrochlore powders prepared by solid state route. The sintering and dielectric properties of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics are investigated, which show that the sintering temperature of the prepared ceramics could be effectively lowered to 800°C and the bulk density reach 6.889 g/cm³ approximately 97% of the theoretical density of Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics. The excellent dielectric properties of the ceramics sintered at 850°C has been obtained with the relative permittivity of 160 and the dielectric loss of 10^?4. This route would be a low-cost and mass production for lowering the sintering temperature of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics without sintering aids.