Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

Co-Modification of Ba5NdTi3Ta7O30 Dielectric Ceramics by Substitution and Introducing Secondary Phase

Co-modification of Ba₅NdTi₃Ta₇O₃₀ dielectrics ceramics was investigated through Pb substitution for Ba and introducing Bi₄Ti₃O₁₂ secondary phase. The dielectric constant increased from 150 to 283, the temperature coefficient of the dielectric constant decreased from –2500 ppm/°C to –1279 ppm/°C, and the dielectric loss decreased to 0.0007 at 1 MHz. Meanwhile, the bi-phase ceramics were investigated to achieve temperature stable ceramics with high dielectric constant and low dielectric loss. As the composition x varied from 0.4 to 0.7 for (1 – x)(Ba_0.8Pb_0.2)₅NdTi₃Ta₇O₃₀/xBi₄Ti₃O₁₂, the temperature coefficient of the dielectric constant changed from negative to zero to positive.     

Characteristics of Bi4Ti3O12 thin films on ITO/glass and Pt/Si substrates prepared by R.F. sputtering and rapid thermal annealing

Bi₄Ti₃O₁₂ thin films are deposited on ITO/glass and Pt/Ti/Si(100) substrates by R.F. magnetron sputtering at room temperature. The films are then heated by a rapid thermal annealing (RTA) process conducted in oxygen atmosphere at temperatures ranging from 550–700^∘C. X-ray diffraction examination reveals that the crystalinity of the films grown on Pt/Ti/Si is better than that of the films grown on ITO/glass under the same fabrication conditions. SEM observation shows that the films grown on Pt/Ti/Si are denser than those grown on ITO/glass substrates. Interactive diffusion between the Bi₄Ti₃O₁₂ film and the ITO film increases with the increase of annealing temperature. The optical transmittance of the thin film annealed at 650^∘C is found to be almost 100% when the effect of the ITO film is excluded. The relative dielectric constants, leakage currents and polarization characteristics of the two films are compared and discussed.     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

Nanocomposite ceramics based on La-doped BaTi2O5 and BaTiO3 with high temperature-independent permittivity and low dielectric loss

Nanocomposite ceramics containing a mixture of two ferroelectric phases, La-doped BaTi₂O₅ and BaTiO₃, with carefully-controlled phase amounts and ceramic microstructure have temperature-independent permittivity and low dielectric loss over very wide temperature ranges: ɛ = 95 ± 10 from 25 to 600 °C; tan δ = 0.02(2) from 25 to 400 °C, measured at 100 kHz. Further optimisation of properties should be possible.     

Effects of molten salt synthesis (MSS) parameters on the morphology of Sr3Ti2O7 and SrTiO3 seed crystals

A two-step molten salt synthesis process was utilized to fabricate Sr₃Ti₂O₇ and SrTiO_3. High aspect ratio SrTiO₃ seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type in a systematic fashion. Sr₃Ti₂O₇ seeds were synthesized at temperatures ranging from 1050–1350°C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various salt types, including NaCl, KCl, and a 1:1 combination of NaCl and KCl. Sr₃Ti₂O₇ seeds synthesized at 1250°C with a 1:1 salt-to-oxide ratio in 100% NaCl salt resulted in a majority of higher aspect ratio platelets and elongated platelets as opposed to lower aspect ratio cubic-like and tetragonal-like morphologies. The seeds were 10–40 μm in length with aspect ratios of highly elongated platelets as high as 25:1. A second MSS step was used to synthesize SrTiO₃ seeds of the proper composition by TiO₂ addition to the Sr₃Ti₂O₇ seeds and heat treatment at 1100°C. These studies showed that highly anisotropic SrTiO₃ seeds could be produced at 1250°C using a 1:1 salt-to-oxide ratio in 100% NaCl flux. XRD studies of the resulting SrTiO₃ seeds revealed that the increase in aspect ratio for these particular seeds also resulted in the enhancement of (200) peaks, which are of major interest for texturing of PMN-PT.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

Flux-mediated epitaxy for ferroelectric Bi4Ti3O12 single crystal film growth

We propose the “Flux-mediated epitaxy” as a novel concept for the growth of single crystalline films of incongruent, volatile, and high-temperature-melting compounds. In flux-mediated eptitaxy, by supplying materials precursors from the gas phase through the liquid flux films pre-deposited on the substrate, a quasi-thermodynamic equilibrium condition is obtained at the interface between the growing films and the flux films. This process has been demonstrated in this paper by fabricating ferroelectric Bi₄Ti₃O₁₂ films, which has volatile Bi oxide. The most important step in this process is the selection of the right flux material, which is hard to predict due to the lack of an appropriate phase diagram. In order to overcome this problem, we have selected the combinatorial approach. A series of ternary flux libraries composed of two self-fluxes (Bi₂O₃ and Bi₄Ti₃O₁₂) and a third impurity flux were fabricated on SrTiO₃ (001) substrates. After that, stoichiometric Bi₄Ti₃O₁₂ films were grown on each of these flux libraries at a temperature presumed to melt the flux. High-throughput characterization with the concurrent X-ray diffraction method resulted in the identification of CuO containing Bi₂O₃ as the flux material for the growth of single crystalline Bi₄Ti₃O₁₂ films. Stoichiometric Bi₄Ti₃O₁₂ films fabricated by using a novel CuO containing Bi₂O₃ are qualified to be single crystalline judging from their large grain size and the electrical properties equivalent to bulk single crystal’s.     

Low temperature sintering and microwave dielectric properties of Ba3Ti5Nb6O28 with B2O3 and CuO additions

The low sintering temperature and the good dielectric properties such as high dielectric constant (ε _r ), high quality factor (Q × f), and small temperature coefficient of resonant frequency (TCF) are required for the application of chip passive components in wireless communication low temperature co-fired ceramics (LTCC). In the present study, the sintering behaviors and dielectric properties of Ba₃Ti₅Nb₆O₂₈ ceramics were investigated as a function of B₂O₃-CuO content. The pure Ba₃Ti₅Nb₆O₂₈ system showed a high sintering temperature (1250^∘C) and had the good microwave dielectric properties: Q × f of 10,600 GHz, ε _r of 37, TCF of −12 ppm/^∘C. The addition of B₂O₃-CuO was revealed to lower the sintering temperature of Ba₃Ti₅Nb₆O₂₈, 900^∘C and to enhance the microwave dielectric properties: Q × f of 32,500 GHz, ε _r of 40, TCF of 9 ppm/^∘C. From the X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) studies, these phenomena were explained in terms of the reduction of oxygen vacancies and the formation of secondary phases having the good microwave dielectric properties.     

Fatigue Melioration of Neodymium-Modified Bi4Ti3O12 Ceramics

Pure and Nd-modified Bi₄Ti₃O₁₂ ceramics were prepared using the conventional solid state reaction method and their dielectric properties and mechanical properties are investigated. It shows that the activation energy of oxygen vacancies is enhanced whereas the concentration of oxygen vacancies is reduced when Bi³⁺ ions are partially substituted by Nd³⁺ ions. The Cole-Cole fitting to the dielectric loss reveals a strong correlation among oxygen vacancies. The strong correlation reduces the activation energy of oxygen vacancies efficiently. Therefore, we conclude that the diluted oxygen vacancies concentration is the origin of the excellent fatigue resistance of Nd-modified Bi₄Ti₃O₁₂ materials.     

Preparation of Bi4Ti3O12 thin films by electron cyclotron resonance sputtering

Abstract

Ferroelectric Bi₄Ti₃O₁₂ thin films were deposited on Pt-coated oxidized Si substrate by electron cyclotron resonance (ECR) sputtering using ceramic targets. Crystal structure and dielectric properties of the films were investigated as functions of sputtering conditions such as substrate temperature and sputtering gas. Using a target with excess Bi content compared to stoichiometric composition was required to compensate Bi re-evaporation from the substrate and to obtain a perovskite single phase at 600°C. (117)-oriented films exhibited ferroelectric hysteresis loops. The remanent polarization and coercive field of the films were 9.8 μC/cm² and 180 kV/cm, respectively.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Thermal and dielectric properties of ZnO-B2O3-MO3glasses (M = W, Mo)

Glasses in the ZnO-B₂O₃-MO₃(M = W, Mo) ternary were examined as potential replacements to PbO-B₂O₃-SiO₂-ZnO glass frits with the low firing temperature (500–600^∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150^∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition temperature (T _g ), softening temperature (T _d ), the coefficient of thermal expansion (CTE), dielectric constant (ε _r ), and optical property. The glass transition temperature of the glasses varied between 470 and 560^∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10^{− 6}/^∘C and 8–10, respectively. The addition of MO₃to ZnO-B₂O₃binary could induce the expansion of glass forming region, the reduction of T _g and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO₃to ZnO-B₂O₃binary on the transmittance in the visible-light region (350–700 nm) was investigated.     

Dielectric relaxation phenomenon of rare earth Nd3+ modified bismuth layer ferroelectric ceramics fabricated by plasma active sintering method

Abstract

The crystalline structure, dielectric relaxation and ferroelectric properties of the solid solution, Nd _x Bi_4-x Ti₃O₁₂ (NBIT) compound were measured. The Curie temperature of the NBIT ceramics was determined to be 490°C from dielectric measurements. The dielectric constant of the NBIT ceramics shows a small anisotropic property. Polarization switching was observed using a Sawyer-Tower circuit at 50 Hz. Remnant polarizations and coercive fields could not be confirmed since the hysteresis loops were not saturated. The large dielectric relaxation is observed in the frequency range between 100 kHz and 1 MHz.     

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.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Temperature-Stable High-ε Dielectrics Ceramics Based on (1 − x) Ba5NdTi3Ta7O30/xBi4Ti3O12

Modification of Ba₅NdTi₃Ta₇O₃₀ dielectric ceramics was investigated through introducing Bi₄Ti₃O₁₂. With increasing of Bi₄Ti₃O₁₂ content, the dielectric constant increased, and the temperature coefficient of the dielectric constant changed from negative to positive. The small temperature coefficient ( < 50 ppm/°C) combined with high dielectric constant ( = 178) and low dielectric loss (tan = 0.007 at 1 MHz) was achieved in the composition x = 0.6.     

Dielectric properties of Pb[(Mg1/3Nb2/3),Ti]O3 with Bi modification

Bi(Mg_2/3Nb_1/3)O₃ was partially substituted into a Pb(Mg_1/3Nb_2/3)O₃⋅PbTiO₃ perovskite system and resultant changes in the phase developments and dielectric properties were investigated. Two major structures of columbite and rutile, along with a small fraction of Mg₄Nb₂O₉ (α-Al₂O₃ structure), were developed in the B-site precursor system, whereas only a perovskite was observable after the addition of PbO and Bi₂O₃. The replacement of Bi for Pb resulted in a great reduction in the maximum dielectric constants as well as a substantial decrease in the dielectric maximum temperatures.     

Low-temperature sintering and electrical properties of (1−x)Pb(Zr0.5Ti0.5)O3-xPb(Cu0.33Nb0.67)O3 ceramics

Electrical properties and sintering behaviors of (1 − x)Pb(Zr_0.5Ti_0.5)O₃-xPb(Cu_0.33Nb_0.67)O₃ ((1 − x)PZT-xPCN, 0.04 ≤ x ≤ 0.32) ceramics were investigated as a function of PCN content and sintering temperature. For the specimens sintered at 1050^∘C for 2 h, a single phase of perovskite structure was obtained up to x = 0.16, and the pyrochlore phase, Pb₂Nb₂O₇ was detected for further substitution. The dielectric constant (ε _r), electromechanical coupling factor (K_p) and the piezoelectric coefficient (d ₃₃) increased up to x = 0.08 and then decreased. These results were due to the coexistence of tetragonal and rhombohedral phases in the composition of x = 0.08. With an increasing of PCN content, Curie temperature (T_c) decreased and the dielectric loss (tanδ) increased. Typically, ε_r of 1636, K_p of 64% and d₃₃ of 473pC/N were obtained for the 0.92PZT-0.08PCN ceramics sintered at 950^∘C for 2 h.     

Conduction mechanism of grain oriented Bi3.15Nd0.85Ti3O12 ceramics fabricated by a hot-forging method

We have fabricated ordinary fired (OF) and grain oriented Bi_3.15Nd_0.85Ti₃O₁₂ (HF[⊥], HF[//]) samples by a hot-forging technique. The grain orientation factor F calculated from X-ray diffraction patterns of the c-axis oriented Bi_3.15Nd_0.85Ti₃O₁₂-HF[//] sample is determined to be above 90%. The dielectric and ferroelectric properties of Bi_3.15Nd_0.85Ti₃O₁₂ ceramics with different grain orientation have been investigated as a function of temperature. The a-b axis oriented Bi_3.15Nd_0.85Ti₃O₁₂-HF[⊥] sample had an enhanced dielectric constant (1163 at T _c) and ferroelectric properties (P _r ∼ 32 μC/cm²). The electrical conductivity of BNT ceramic has been studied as a function of temperature in order to investigate the conduction mechanism with different grain orientations.