Ferroelectric Bi4Ti3O12 and Bi4−x La x Ti3O12 ceramics prepared by a new sol-gel route

Ceramics of bismuth titanate, Bi₄Ti₃O₁₂ (BIT) and the La-doped series, Bi_4?x La _x Ti₃O₁₂ (xBLT) with x?=?0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.75, have been synthesized by a new sol-gel process based on ethylene glycol. La-doping is found to reduce the temperature of the formation of pure Bi-layer-structured phase from 600 °C in BIT and low La-doped xBLT (x?=?0.1–0.3) to 500 °C in high La-doped xBLT (x?=?0.4–0.75). Increasing the La-content in the xBLT ceramics decreases the contribution of the space charge polarization to the apparent dielectric permittivity. The ceramics of xBLT prepared by this sol-gel route exhibit improved dielectric properties, with a higher room temperature dielectric constant and lower losses up to high temperatures.     

Ferroelectric Characteristics of Bi 4−x La x Ti 3 O 12 Thin Films Crystallized at Low Temperetures

Recently, Bi 4 m x La x Ti 3 O 12 (BLT) has received much attention because it enables low crystallization temperature with a large remanent polarization. BLT films were prepared using a metal organic decomposition technique followed by a rapid thermal annealing (RTA) and a furnace annealing. The annealing of BLT was performed in the temperature range from 550 to 700C. In particular, BLT film annealed at 600C using the RTA tool and the furnace shows good ferroelectric characteristics. The BLT film annealed at 600C exhibits a large value of remanent polarization (22 w C/cm 2 at 250kV/cm), and a low leakage current density (7 2 10 m 7 A/cm 2 at 250kV/cm), a good endurance characteristics for up to 3.2 2 10 11 cycles at 250kV/cm at 85C. From an accelerated imprint test, the lifetime of hysteresis integrity is estimated to be over 10 years at 85C. In conclusion, BLT is the one of the promising material to achieve the high density FeRAMs.     

Effect of B2O3 Nano-Coating on the Sintering Behaviors and Electrical Microwave Properties of Ba(Nd2 − x Sm x )Ti4O12 Ceramics

Ba(Nd_0.8Sm_0.2)₂Ti₄O₁₂ ceramics prepared by conventional solid-state sintering have a dielectric constant of about 80 and a nearly zero temperature coefficient of resonant frequency; however, the sintering temperature is above 1350_C. Doping with B₂O₃ (up to 5 wt%) promotes the densification and dielectric properties of BNST ceramics. It is found that coating BNST powder with thin B₂O₃ layer of about 180 nm reduces the sintering temperature to below 1020_C. The effects of B₂O₃ nano-coating on the dielectric microwave properties and the microstructures of BNST ceramics are investigated. Ninety-six percent of theoretical densities is obtained for specimens coated with 2 wt% B₂O₃ sintered at 960_C and the samples exhibit significant (002) preferred orientation and columnar structure.     

Preparation and Properties of Bi4 − x Nd x Ti3O12 Thin Films by Chemical Solution Deposition

Neodymium-modified Bi₄Ti₃O₁₂, (Bi, Nd)₄Ti₃O₁₂ (BNT) ferroelectric thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates using metal-organic precursor solutions by the chemical solution deposition method. The BNT precursor films crystallized into the Bi layered perovskite Bi₄Ti₃O₁₂ (BIT) as a single-phase above 600C. The synthesized BNT films revealed a random orientation having a strong 117 reflection, whereas non-substituted BIT thin films exhibited a random orientation with strong 00l diffractions. Among Bi_{4 – x}Nd_xTi₃O₁₂ [x = 0.0, 0.5, 0.75, 1.0] thin films, Bi_3.25Nd_0.75Ti₃O₁₂ thin films showed a well-saturated P-E hysteresis loop with the highest P_r (22 C/cm²) and a low E_c (69 kV/cm) at an applied voltage of 5 V. The Nd-substitution with the optimum amount for the Bi site in the BIT structure was effective not only for promoting the 117 preferred orientation but also for improving the microstructure and ferroelectric properties of the resultant films.     

Chemical Vapor Deposition of Ru Bottom Electrode for Ferroelectric Bi4 − x La x Ti3O12 Capacitors

Ruthenium films formed by metalorganic chemical vapor deposition were investigated, taking account of the application to the bottom electrode of ferroelectric capacitors. Ruthenium films were deposited using a liquid-type source of Ru[EtCp]₂ in a cold-wall type reactor with infrared lamps. A smooth and flat Ru film was successfully formed on a SiO₂-covered Si substrate without a seed layer. As the deposition temperature increased to 400°C, the crystallinity of the Ru film improved and the film exhibited high c-axis orientation. After forming a Bi_{4 ? x} La _x Ti₃O₁₂ (BLT) film by a sol-gel technique, a Pt/BLT/Ru capacitor was fabricated on the Ru film. Good hysteresis loops with 2P _r = 20 μC/cm² and 2V _c = 3.4 V were successfully obtained and the ferroelectric property did not depend on the deposition temperature of Ru in the temperature range from 325°C to 400°C. On the contrary, the leakage current density was significantly suppressed down to 1/100 as the deposition temperature of Ru increased from 325°C to 400°C.     

Synthesis and Ferroelectric Response of Bi 4−x Nd x Ti 3 O 12 Thin Films

Nd doped Bi 4 Ti 3 O 12 layered materials were synthesized using a solution chemistry route. Thin films were deposited by spin coating. Powder and thin film samples were characterized by x-ray diffraction and Raman spectroscopy. Ferroelectric response of Bi 4 m x Nd x Ti 3 O 12 thin film (x = 0.95), deposited on Pt substrate is reported.     

Piezoelectric and Dielectric Properties of Pb(Zr x Ti1 − x )O3-Pb(Ni1/3Sb1/3Nb1/3)O3 Piezoelectric Ceramics

In this paper, piezoelectric and dielectric properties of 0.9PbZr_xTi_1–xO₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃ were studied as a function of Zr/Ti mole ratio(x) for application to piezoelectric actuator. Also, microstructure and crystalline phase are investigated by using SEM and XRD, respectively. As a results, the substitution of Sb5+ to B-site increases the piezoelectric and dielectric properties, and when Zr/Ti mole ratio is 49/51 and ternary mole ration is 0.1(0.9PbZr_0.49Ti_0.51O₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃), the corresponding composition were found belonging to the Morphotropic Phase Boundary region with electromechanical coupling coefficient(k_p), mechanical quality factor (Q_m), permittivity(_r) and piezoelectric strain constant(d₃₃) equaled to 63%, 360, 2000 and 470 pC/N, respectively. Sintering temperature was about 1150_C and Curie temperature was determined around 290_C.     

Microwave Dielectric Properties of Ferroelectric Pb(Zr1 − x Ti x )O3 Thin Films Using Interdigital Capacitors

Ferroelectric Pb(Zr_{1 ? x} Ti _x )O₃ (PZT) films were deposited on (001) MgO single crystals using sol-gel method. Structural properties and surface morphologies of PZT films were investigated using an X-ray diffractometer and a scanning electron microscopy, respectively. The dielectric properties of PZT films were investigated with the dc bias field of 0–135 kV/cm using interdigitated capacitors (IDC) which were fabricated on PZT films using a thick metal layer by photolithography and etching process. The small signal dielectric properties of PZT films were calculated by a modified conformal mapping method with low and high frequency data, such as capacitance measured by an impedance gain/phase analyzer at 100 kHz and reflection coefficient (S-parameter) measured by a HP 8510C vector network analyzer at 1–20 GHz. The IDC on PZT films exhibited about 67% of capacitance change with an electric field of 135 kV/cm at 10 GHz. These PZT thin films can be applied to tunable microwave devices such as phase shifters, tunable resonators and tunable filters.     

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.     

Synthesis and Dielectric Characterization of Pyrochlore-Free Pb1−x Ba x (Zn1/3Nb2/3)O3 Ceramics

The dielectric properties and synthesis of pyrochlore-free lead zinc niobate ceramics with Ba substituting for Pb were investigated. Ba partial substitution for Pb was effective in stabilizing the perovskite structure in PZN ceramics, where the minimum amount of Ba substitution needed was about 20 mol%. The dielectric loss and the temperature coefficient of dielectric constant of PZN were reduced markedly with Ba substitution, while the dielectric constant was greater than 110. Good dielectric properties were obtained for the composition of Pb_0.3Ba_0.7(Zn_1/3Nb_2/3)O₃: = 133.5, tan = 0.0009, = –811 ppm/°C.     

Structure and dielectric properties of Bi5−x La x Nb3O15 ceramics

Bi_5?x La _x Nb₃O₁₅ (x?=?0–?1.25) ceramics prepared by conventional solid-state reaction were studied using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and dielectric spectroscopy techniques. The XRD analysis indicated single phase solid solution of Bi_5?x La _x Nb₃O₁₅ is formed for x?≤?1.25. EPMA showed good densification and homogeneous microstructures for the ceramics. With increasing x, the dielectric constant decreases monotonously and can vary from 258 to 158 at 300 kHz. The frequency dependence of dielectric constants indicated these ceramics are promising candidates for high frequency 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.     

Properties of CaTi1 − x Fe x O3 − δ Ceramic Membranes

CaCO₃, TiO₂ and Fe₂O₃ were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi_{1 – x}Fe_xO_3– (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_C. The estimated linear thermal expansion coefficient is close to 13× 10^{– 6} K^{– 1} and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO₂ atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi_0.80Fe_0.20O_3– is compared to other mixed conducting materials.     

Scaling Effect on the Dielectric Constant in Ba(Ti x Zr1−x )O3 Thin Films

Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(Ti_xZr_{1 – x})O₃ thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.     

Low-temperature sintering and dielectric properties of the Bi(Nb1−x Ta x )O4 system

Low-temperature sintering and dielectric properties of the Bi(Nb_1?x Ta _x )O₄ (x?=?0.1, 0.3, and 0.5) system was investigated as a function of the zinc borosilicate (ZBS) glass content with a view to applying this system to LTCC technology. The addition of 7 wt% ZBS glass ensured a successful sintering below 900°C. The complete solid solution of Bi(Nb, Ta)O₄ with an orthorhombic structure was formed and the high temperature form of Bi(Nb, Ta)O₄ with a triclinic structure was not observed. The second phase of Bi₂SiO₅ was observed for all compositions. The non-relative liquid phase sintering (NLPS) occurred and the one-stage sintering was conducted. The Q?×?f values were improved by the addition of Ta. Bi(Nb_0.7Ta_0.3)O₄ with 7 wt% ZBS glass sintered at 900°C demonstrated 35.8 in the dielectric constant (? _r), 2,200 GHz in the quality factor (Q?×?f ₀), and ?48 ppm/°C in the temperature coefficient of resonant frequency (τ _f).     

Dielectric Properties and Phase Transition Behavior of xPMN-(1 − x)PZT Ceramic Systems

The dielectric properties and phase transition behavior of the pseudo-ternary xPb(Mg_1/3Nb_2/3)O₃-(1 – x)Pb(Zr,Ti)O₃ solid solution system were investigated as a function of the Pb(Mg_1/3Nb_2/3)O₃ (PMN) content and Ti/Zr ratio for selected compositions. The investigations have demonstrated a general trend in broadening of the phase transition and increasing diffusivity with increasing PMN content. For the morphotropic phase boundary (MPB) compositions, the dielectric permittivity maximum, its temperature (T _m) and the Curie-Weiss constant were found to decrease with increasing Mg_1/3Nb_2/3 concentration. When a Ti/Zr ratio was constant and equal to 53/47, temperature-dependent investigations demonstrated that the dielectric parameters involved in a modified Curie-Weiss law increase monotonically with increasing PMN content and T _m moves toward room temperature with average rate of –4.1°C/mol% as well. A phase transition in 0.5PMN-0.5Pb(Zr_0.47Ti_0.53)O₃ and 0.25PMN-0.75Pb(Zr_0.60Ti_0.40)O₃ ceramic systems exhibited a diffused behavior with a characteristic frequency dependence of T _m. From pyroelectric measurement, an unusual spontaneous polarization behavior at about 215 K is reported for some MPB compositions.     

锂离子电池正极材料Li3+xV2(PO4)3-x(SiO4)x(0≤x≤0.3)合成及电化学性能

采用溶胶凝胶结合碳热还原法制备了一种新型锂离子电池正极材料.该材料中,硅酸根取代了磷酸钒锂中的部分磷酸根,得到组成为Li3+xV2(PO4)3-x(SiO4)x(0≤x≤0.3)的材料.采用沥青作为碳源,碳既是还原剂又作为导电剂.比较了x=0,0.05,0.1,0.2,0.3时,材料的库仑效率,容量和循环性能.当x=0...     

Thermoelectric properties of Ca3-xEuxCo3.95Ga0.05O9+δ (0 ≤ x ≤ 0.10)

Polycrystalline samples of Ca_3–xEu_xCo_3.95Ga_0.05O_9+δ (x?=?0.00, 0.02 and 0.10) have been prepared by conventional solid-state synthesis and their thermoelectric properties measured at 25 K to 300 K. The XRD results revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were simultaneously increased with increasing Eu³⁺ content. The total thermal conductivity decreased with increasing Eu³⁺ content. A maximum dimensionless figure of merit of 0.033 at 300 K was reached for Ca_2.9Eu_0.1Co_3.95Ga_0.05O_9+δ, which is about 27 % higher than that of the undoped sample. These results suggest that the Eu is an effective doping element for improving the thermoelectric properties of Ca₃Co_3.95Ga_0.05O_9+δ.     

Microstructural Design and Properties of LaCoO3/La2(Zr,Y)2O7−δ Composites

LaCoO_3–/La₂(Zr,Y)₂O₇-based composites were designed in view of three main properties: electrical conductivity, thermal expansion and resistance to thermal cycling. Composition and processing conditions were investigated on the basis of an experimental plan according to the Taguchi method. The phase distribution was estimated from image analysis and related to electrical and thermo-mechanical behavior. Results indicate that an homogeneous and fine grained phase distribution is essential in order to obtain materials with the desired thermal expansion, electrical properties and thermomechanical properties.     

(Reactive) Templated Grain Growth of Textured Sodium Bismuth Titanate (Na1/2Bi1/2TiO3-BaTiO3) Ceramics—II Dielectric and Piezoelectric Properties

(Na_1/2Bi_1/2)TiO₃-BaTiO₃ (<6.5% BaTiO₃) ceramics with <001>_pc orientation were fabricated by Templated Grain Growth (TGG) or Reactive Templated Grain Growth (RTGG) using tabular SrTiO₃ template particles. The maximum electrically-induced strain was 0.26% at 70 kV/cm. d₃₃ coefficients over 500 pC/N were obtained for highly textured samples (f 90%) when driven at high electric fields. Under these conditions, the materials show considerable hysteresis in the strain—field response, even after poling. Berlincourt piezoelectric coefficients for the same samples gave d₃₃ of 200 pC/N.