Dielectric Properties and Sintering Characteristics of CaTiO<Subscript>3</Subscript>-(Li<Subscript>1/2</Subscript>Nd<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ceramics

The dielectric properties and the sintering effect upon microstructure of (1–x) CaTiO₃-x(Li_1/2Nd_1/2)-TiO₃ Ceramics are investigated in this paper. Nd³⁺ and Mg^{2 +} ions co-substitution for Ca^{2 +} on A site improves the sintering characteristic of CaTiO₃ ceramics with forming orthorhombic perovskite structure. The structure of (1 – x) CaTiO₃-x(Li_1/2Nd_1/2)TiO₃ changes from orthorhombic to tetragonal as (Li_1/2Nd_1/2)TiO₃ addition increasing. Limited solubility of (Li_1/2Nd_1/2)TiO₃ in CaTiO₃ forming a part solid solution compound achieves the adjustment of for CaTiO₃ at low sintering temperature. The proper dielectric properties with = 78, tan = 0.0006, = +7 ppm/C are obtained for 0.8Ca_0.67(Nd,Mg)_0.22TiO₃-0.2(Li_1/2Nd_1/2)TiO₃ ceramics.     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Dielectric and Piezoelectric Properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-NaNbO<Subscript>3</Subscript>Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 – x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃] – xNaNbO₃(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant _r and dissipation factor tan measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures T_d and T_m are lowered due to introduction of NaNbO₃. P-E hysteresis loops show that 0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃ ceramics has the maximum P_r and E_c corresponding to the maximum values of electromechanical coupling factor K_p and piezoelectric constant d_33. The piezoelectric constant d₃₃ and electromechanical coupling factor K_p decrease a little, while the dielectric constant ₃₃^T/₀ improves much more when the concentration of NaNbO₃ is 8 mol%.     

Microwave Dielectric Properties of CuO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

Microwave dielectric properties of low temperature sintering ZnNb₂O₆ ceramics doped with CuO-V₂O₅-Bi₂O₃ additions were investigated systematically. The co-doping of CuO, V₂O₅ and Bi₂O₃ can significantly lower the sintering temperature of ZnNb₂O₆ ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V₂O₅-Bi₂O₃ content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( _r) of ZnNb₂O₆ ceramics increased from 21.95 to 24.18 with increasing CuO-V₂O₅-Bi₂O₃ additions from 1.5 to 4.0 wt%. The quality factors (Q× f) of this system decreased with increasing CuO-V₂O₅-Bi₂O₃ content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q× f values of samples with CuO-V₂O₅-Bi₂O₃ additions are lower than that of un-doped ZnNb₂O₆ ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( _f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V₂O₅-Bi₂O₃ from 1.5 to 4.0 wt%     

Tunable Dielectric Characteristics of 0.9Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>/0.1CaTiO<Subscript>3</Subscript>

Tunable dielectric characteristics of 0.9Pb(Fe_1/2Nb_1/2)O₃/0.1CaTiO₃ relaxor ferroelectric ceramics were investigated as the function of DC bias field and temperature. High tunability (more than 20%) was obtained in the present ceramics under a relatively weak DC bias field (1.4 kV/cm). The value of tunability changed from negative to positive with increasing DC field. For the simulation of the dielectric constant under DC bias field, modified model needs to be constructed for the relaxor ferroelectrics. The dielectric constant curve as a function of temperature without and under DC field was well fitted using the equation of diffuse phase transition. The lower ε_max, higher T_max and higher diffuseness parameter under DC field were observed and only the lower ε_max contributed to positive tunability.     

Low Temperature Sintering of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-Based Middle-<Emphasis Type="Italic">k</Emphasis> Dielectric Composition for LTCC Applications

Effect of glass addition on the low-temperature sintering and microwave dielectric properties of BaTi₄O₉-based ceramics were studied to develop the middle-k dielectric composition for the functional substrate of low-temperature co-fired ceramics. When 10 wt% of glass was added, sufficient densification was obtained and the relative density more than 98% was reached at the sintering temperature of 875C. The microwave dielectric properties were k = 32, Q × f = 9000 GHz, and t_cf = 10 ppm/C. As the added amount of glass frit with base dielectric composition, phase changes from BaTi₄O₉ to BaTi₅O₁₁ and Ba₄Ti₁₃O₃₀ was observed, which result in the modification of microwave dielectric properties.     

Effects of MnO<Subscript>2</Subscript> addition on microstructure and electrical properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>) <Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.     

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.     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Effect of SiO<Subscript>2</Subscript> Addition to BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass on Dielectric and Thermal Properties for Application to Barrier Ribs of Plasma Display Panels

The effect of SiO₂ addition to barium zinc borate (BaO-ZnO-B₂O₃, BZB) glass on dielectric and thermal expansion properties was investigated. When SiO₂ was added to the glass batch to form a SiO₂-BaO-ZnO-B₂O₃ (SBZB) glass, the dielectric constant decreased significantly from 15.5 to 9.9. When SiO₂ (quartz) was further added to the SBZB in the form of filler particles to yield ceramic filler-reinforced SBZB microcomposites, the dielectric constant was further decreased. The coefficient of thermal expansion (CTE) of SBZB was slightly lower than the allowable range, while the filler addition to SBZB correspondingly increased CTE to the allowable range. Thus, the addition of SiO₂ to BZB glass to form SBZB glass and further addition to SBZB in the form of ceramic filler were shown to be amenable ways to tailor the dielectric constant as well as CTE of the barrier rib glass for the PDP application.     

Dielectric and Ferroelectric Characterization of Na(Ta,Nb)O<Subscript>3</Subscript> Solid Solution Ceramics

Ceramics in the Na(Ta_{1 − x}Nb_x)O₃ system were prepared by a solid state reaction approach, and their dielectric characteristics were evaluated together with the structures. The complete solid solution with orthorhombic structures was observed in the present system, and three supposed phase transitions at about 475, 580 and 650^∘C were observed by DTA. Only one dielectric anomaly was observed at high temperature for x = 0.2 and 0.4, and alternative dielectric anomaly (a diffused dielectric peak) was observed around 170 and 380^∘C for x = 0.6 and 0.8, respectively. The compositions of 0.6 and 0.8 are weakly ferroelectric and those of 0.2 and 0.4 are supposed to be antiferroelectric at room temperature.     

Site Preference of La in Bi<Subscript>3.75</Subscript>La<Subscript>0.25</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Using Neutron Powder Diffraction and Raman Scattering

Both structural refinement using neutron powder diffraction data and Raman scattering were carried out to determine the site preference of La atoms and the cation distribution in Bi_3.75La_0.25Ti₃O₁₂ compound. Of three possible cation-disorder models, the best structural refinement result was obtained from a model that La atoms substitute only for Bi atoms outside of the TiO₆ octahedra in the Bi₂Ti₃O₁₀ unit. The model proposed by the structural refinement was corroborated by the Raman spectroscopic study. The final weighted R-factor, R_wp, and the goodness-of-fit indicator, S (= R_wp/R_e), based on the neutron diffraction and the Raman scattering were 4.12% and 1.43, respectively. The occupancy of La atoms for two Bi sites in the perovskite-like unit was 0.082 and 0.074, respectively. The refined model described a structure in monoclinic space group B1a1 with Z = 4, a = 5.4387(1) Å, b = 5.4129(1) Å, c = 32.8441(1) Å and = 90.03(1).     

Excellent dielectric constants observed in heterogeneous conduction Ba(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> ceramics doped with Sr(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>

The (1-x)Ba(Zr_0.25Ti_0.75)O₃-xSr(Fe_0.5Nb_0.5)O₃ or (1-x)BZT-xSFN ceramics have been fabricated via a solid-state reaction technique. All ceramics exhibit a pure phase perovskite with cubic symmetry. The addition of a small amount of SFN (x?=?0.1) produces an obvious change in dielectric behavior. Very high dielectric constants (ε_r?>?164,000 at 1 kHz and temperature?>?150°C) are observed and the value is obviously higher than dielectric constants for Ba(Zr_0.25Ti_0.75)O₃ and Sr(Fe_0.5Nb_0.5)O₃ ceramics. The ferroelectric measurement data suggests that the unmodified sample exhibited a ferroelectric behavior. However, a transformation from a ferroelectric to a relaxor-like behavior is noted with increasing x concentration. Impedance Spectroscopy (IS) analysis indicates that the presence of excellent dielectric constants is due to the heterogeneous conduction in the ceramics after adding SFN, which can be explained in terms of the Maxwell-Wagner polarization mechanism.     

Dielectric properties and defect mechanisms of (1-<Emphasis Type="Italic">x</Emphasis>)Ba(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> -<Emphasis Type="Italic">x</Emphasis>BiYbO<Subscript>3</Subscript> ceramics

(1-x)Ba(Fe_0.5Nb_0.5)O₃ -xBiYbO₃ (BFN-xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN-xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law.     

The Applicability of Sr-deficient <Emphasis Type="Italic">n</Emphasis>-type SrTiO<Subscript>3</Subscript> for SOFC Anodes

Here we discuss the effect of preparation conditions on structural stability and electrical properties of Sr-deficient n-type SrTiO₃. In particular, an explanation of a wide scatter of conductivity values in Y- and Nb-doped SrTiO₃. reported in the literature is proposed, based on the existing defect chemistry model of n-doped SrTiO₃. It was confirmed that when sintered in air, Sr-deficient SrTiO₃ doped with Nb and/or Y, remains single phase until the solubility limit (e.g., 30% for Nb or 4% for Y). However, when sintered at low po₂, the material transforms from a vacancy compensated to an electronically compensated compound with a strontium deficient second phase. Measured at 800°C in low po₂, the maximum conductivity of these multi-phase compounds was 340 S/cm and 100 S/cm for the Nb-doped and Y-doped sample, respectively. However, the conductivity dropped dramatically to less than 10 S/cm when samples of the same compositions were sintered in air, again measured in reducing atmosphere.     

Electrical characterizations of MgTiO3 thin films grown on Si

Abstract

We have analyzed MgTiO₃ thin films grown on the Si substrate with/without SiO₂ using pulsed laser deposition (PLD). We find that MgTiO₃ thin films start to crystallize at 600°C, causing electrical instabilities in the MIS capacitors above this temperature. Detailed analysis by XRD technique reveals that structural differences of MgTiO₃ thin films were not obvious below 600°C, whereas the electrical characteristics changes as a function of deposition temperature and the presence of thermally grown SiO₂. We observe that the decrease of deposition temperature results in the increase of leakage current and anomalous positive charge (APC) density. These drawbacks were effectively suppressed by growing 100A SiO₂ layer on the Si substrate prior to the deposition of MgTiO₃ thin films.     

Lead-free (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)<Subscript>0.95</Subscript>(LiSb)<Subscript>0.05</Subscript>Nb<Subscript>0.95</Subscript>O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> piezoceramics

Lead-free (1-x)(K_0.5Na_0.5)_0.95(LiSb)_0.05Nb_0.95O₃-xBaTiO₃ (abbreviated as (1-x)KNNLS-xBT) piezoceramics were synthesized by conventional solid state sintering and the effect of BaTiO₃ on the microstructure, dielectric and piezoelectric properties was investigated. It was found that both orthorhombic-tetragonal (T _O-T) and tetragonal-cubic (T _C) phase transition temperatures decreased obviously with increasing BaTiO₃ content. Although proper amount of BaTiO₃ facilitated the sintering of (1-x)KNNLS-xBT ceramics, the addition of BaTiO₃ affected the relaxor behavior slightly and it was not beneficial to improve piezoelectric strain coefficient d ₃₃, remnant polarization P _r and piezoelectric coupling constant k _p.     

Piezoelectric Properties of 0.2[Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)]-0.8[PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>] Ceramics Sintered at a Low Temperature with the Aid of Li<Subscript>2</Subscript>O

The dielectric and piezoelectric properties of 0.2Pb(Mg_1/3Nb_2/3)O₃-0.8Pb(Zr_0.475Ti_0.525)O₃ (abbr. as PMNZT) ceramics were measured. Extremely low sintering temperatures of 950^∘C using liquid-phase sintering aid of Li₂O is achieved which was very useful for multi-layered applications. X-ray study shows the splitting of rhombohedral (200) in pure PMNZT to (002) and (200) peaks in Li₂O doped samples. 10 times higher dielectric constant was achieved in Li₂O doped samples to compare to pure ones although the Curie temperature (T_c = 322^∘C) of Li₂O doped PMNZT ceramics was not changed. The value of k_p and k₃₃ increased up to 0.1 wt% of Li₂O and saturating thereafter.     

Structure and properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-0.38PbTiO<Subscript>3</Subscript> ceramics with MPB composition

0.62Bi(Mg_1/2Ti_1/2)O₃-0.38PbTiO₃-xwt%Bi₂O₃ (BMT-0.38PT-xBi₂O₃) ceramics were prepared by conventional powder-processing method. It indicated that the morphotropic phase boundary (MPB) region located in 0.0?≤?x?≤?0.3. For x?=?0.3, it exhibited good piezoelectric properties, d₃₃ ~245pC/N and k_p ~40 %. With the increase of Bi₂O₃ content, the Curie temperature (T_c) was found to increase, and the dielectric loss was found to decrease above 200 °C compared with BMT-0.38PT sample. Finally, it can be found that depolarization temperature was around 350 °C by thermal depoling method.     

(Gd,Co, Ta)-Doped SnO<Subscript>2</Subscript> Varistor Ceramics

The effect on the microstructure and electrical properties of (Co, Ta)-doped SnO₂ varistors upon the addition of Gd₂O₃ was investigated. The threshold electric field of the SnO₂ based varistors increased significantly from 720 V/mm to 1455 V/mm, the relative dielectric constants of the SnO₂ based varistors decreased greatly from 833 to 330 as Gd₂O₃ concentration was increased up to 1.2 mol%. The significant decrease of the SnO₂ mean grain size, from 3.8 to 1.6 m with increasing Gd₂O₃ concentration over the range of 0 to 1.2 mol%, is the origin for increase in the threshold voltage and decrease of the dielectric constants. The mean grain size reduction is attributed to the segregation of Gd₂O₃ at grain boundaries hindering the SnO₂ grains from conglomerating into large particles. Varistors were found to have superhigh threshold voltage and comparatively large nonlinear coefficient . For 0.8 mol% Gd₂O₃-doped sample, threshold electrical field E and nonlinear coefficient were measured to be 1125 V/mm and 24.0, for 1.2 mol% Gd₂O₃-doped sample, E and were 1355 V/mm and 23.0. Superhigh threshold voltage and large nonlinear coefficient qualify the Gd-doped SnO₂ varistor as an excellent candidate in use for high voltage protection system.