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.     

Dielectric relaxation and variable-range-hopping conduction in BaSn1−x Cr x O3 system

The possibility of formation of a solid solution in the system BaSn_1−x Cr _x O₃ has been explored upto x ≤ 0.20. It has been confirmed that single phase solid solution forms upto x ≤ 0.10. Dielectric and conduction behaviour of single phase samples have been studied in the temperature range 400–610 K and frequency range 10 Hz–2 MHz. Two dielectric relaxation processes in two different frequency ranges have been observed. The temperature dependence of both dc and ac resistivity obey relation ρ = ρ _o exp(B/T^1/4), indicative of variable range hopping conduction mechanism. The activation energy for dc conduction is higher than that for relaxation time (τ) of low frequency dielectric relaxation process. It has been observed that activation energy for dielectric relaxation matches with activation energy for ac conductivity (at 100 kHz) for both the dielectric relaxation processes. Seebeck coefficient ‘α’ of the samples have been measured in the temperature range 350–650 K. Negative value of ‘α’ in the entire range of temperature measurement shows that conduction species are negatively charged. On the basis of value of activation energy for dc conduction and sign of Seebeck coefficient, conduction in the low temperature region (below 500 K) is attributed to hopping of weakly bonded electrons among Sn²⁺ ⇔ Sn⁴⁺ or Sn³⁺ ⇔ Sn⁴⁺ and that in the high temperature region (above 500 K) to hopping of doubly ionized oxygen vacancies .     

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.     

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.     

Microstructure dependence of microwave dielectric characteristics in Ba6-3x Sm8+2x Ti18O54 (x = 2/3) ceramics

Effects of microstructures on the microwave dielectric characteristics of Ba_6-3x Sm_8+2x Ti₁₈O₅₄ (x?=?2/3) ceramics were investigated by controlling the sintering process and the annealing condition. The dielectric constant was sensitive to the porosity in ceramics, but insensitive to the annealing process. Q f value varied with both the annealing atmosphere and the sintering temperature, which indicates the strong reliance of dielectric loss on defects and grain boundaries. τ _f value exhibited a complex dependence on the sintering temperature. The orientation of grains is responsible for the variation of τ _f .     

Evaluation of Chemical Solution Deposited Ba x Sr 1−x TiO 3 Thin Films on LaAlO 3 in Tunable Microwave Devices

Epitaxial Ba x Sr 1 m x TiO 3 (BST) films grown on LaAlO 3 by several deposition methods have been tested in coupled microstrip phase shifters (CMPS) at frequencies from 10 to 24 GHz. To date the best performance for the devices has been achieved using Pulsed Laser Deposition (PLD). However, recently chemical solution deposition (CSD) methods such as sol-gel and Metal-Organic Chemical Liquid Deposition (MOCLD) have shown advances in fabricating BST films for tunable microwave applications. CSD processes promise improvements in cost, speed and area covered during BST film deposition. This paper compares over 35 BST films used in identical CMPS circuits. In this study, the highest measured figures of merit of phase shift per dB of loss for PLD, MOCLD and sol-gel CMPS are 49, 47 and 41°/dB respectively. While other phase shifter designs using BST films have surpassed these values, these data base of identical circuits allows us to compare the BST films. X-ray diffraction characterization for many of the BST films is also given.     

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.     

Electrochemical evaluation of La1 − x Ca x CoO3 cathode material for zinc air batteries application

We synthesized nano-sized La_1???x Ca _x CoO₃ (x?=?0.1–0.4) cathode catalysts for zinc air secondary batteries by the citrate method, and measured electrochemical characteristics of the cathodes according to the cathode catalyst’s calcium content. We heat treated the prepared precursor at a calcination temperature of 700°C, and examined it by XRD analysis and electrochemical evaluation. We examined the prepared La_1???x Ca _x CoO₃ catalyst powder’s oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and cycle-stability performance. When we consider ORR, OER and cycle-stability performance simultaneously, La_0.9Ca_0.1MnO₃ catalyst showed the best performance because of its lowest voltage deference between charge and discharge, and its lowest degradation according to cycle.     

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.     

Structure and microwave dielectric properties of La(2−x)/3NaxTiO3

The structure evolution, and microwave dielectric properties of La_(2?x)/3Na_xTiO₃ Ceramics( $ x = 0.02 \leqslant \times \leqslant 0.5 $ ) were investigated in this paper. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that all samples exhibit single phase. The concentration and ordering degree of A-site vacancies decrease with the increase of x value, and no A-site ordering exists when x?>?0.2. The dielectric constant decreases with the decrease of x value. The Q?×?f value increases up to x?=?0.1 and then decreases with the further increase of x value. A maximum Q?×?f value of 18,826 GHz is obtained when x?=?0.06. The temperature coefficient of resonant frequency exhibits positive value and decreases greatly with the decrease of x value.     

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.     

Chemical Solution Deposition of Epitaxial La1−x (Ca, Sr) x MnO3 Thin Films

We report on the epitaxial growth of magnetoresistive La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ thin films by chemical solution deposition. Thin films were prepared by spin-coating of single-crystal LaAlO₃ (100) substrates with precursor solutions of different concentrations and crystallized at 850°C. The structure of the thin film was found to be influenced by the concentration of the spin-coating solution. The thin film structure and epitaxy was clearly improved by reducing the concentration of the precursor solution. All thin films displayed excellent electrical properties such as a low resistivity and very high metal-insulator transition temperatures T _MI .     

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.     

The effects of the LaNiO3 interlayer in the preferential orientation and the dielectrical properties of Ba x Sr1− x TiO3 thin films

Ba _x Sr_1?x TiO₃ (BST) thin films were grown on different substrates with or without LaNiO₃ (LNO) layer by a modified sol–gel process. The BST thin films obtained have full perovskite phase with dense and crack-free surface. BST thin films on different substrates with LNO layer show (100) preferential orientation, the texture coefficient (TC) value is calculated to be about 42.7%, whereas those without LNO layer show a fairly reduced preferential orientation, the TC value is just about 24.8%. It is considered that the preferential orientation is induced by the interface stress between LNO and BST. Electrical property measurements showed that BST thin film with a LNO interlayer has lower capacitance and larger dielectric loss, which is due to smaller grains of the thin film.     

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.     

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.     

Dielectric measurements on a novel Ba1 − x Ca x TiO3 (BCT) bulk ceramic combinatorial library

High-throughput combinatorial methods have the potential to discover new materials. They can investigate the effects of a wide range of dopants on the dielectric properties to optimize existing systems, encouraging the short innovation cycles that industry requires. We are currently part of a consortium of London Universities exploring methods of producing and measuring combinatorial libraries of microwave dielectric ceramics. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce combinatorial libraries consisting of large numbers of sintered bulk ceramic samples with varying composition, on alumna substrates. We have reported the manufacture and characterisation of Ba _x Sr_1???x TiO₃ libraries (x in steps of 0.1) as a proof of concept to demonstrate that the robot works and to confirm a compositional and functional change throughout the libraries, as well as proving that reliable measurements can be made on such small samples. Libraries of Ba_1???x Ca _x TiO₃ samples were made with varying compositions of x?=?0–1 in steps of 0.1, and fired to 1400 °C for 1 h, by LUSI. X-ray diffraction (XRD) data agreed with the few previous reports on this little-studied system, namely that after initially forming a solid solution with Ca addition, above x?=?0.2 a two phase system forms with values of 0.2?<?x?<?0.9, after which a single phase system again appears with values of x?=?0.9 and higher. Dielectric measurements (100 Hz–1 MHz) showed a previously reported unusual initial increase in the Curie point with substitution up to x?=?0.2, followed by a rapid decrease to below 125 K when x?>?0.4. This initial increase has been attributed to the Ca substituting in both the Ba²⁺ A sites and the Ti⁴⁺ B sites of the perovskite up to x?=?0.2, after which T _c decreases greatly as the two phase system forms. Scanning probe microscopy and piezo response force microscopy (PFM) experiments also showed evidence of an increase in piezoelectricity with small amounts of x (0.1–0.2), followed by a decrease with increasing x.     

Dielectric and piezoelectric properties of sodium lithium niobate Na1−x Li x NbO3 lead free ferroelectric ceramics

High density sodium lithium niobate lead free ceramics near the morphtropic phase boundary [Na _x Li_1?x NbO₃, (LNN), x?=?0.12] were prepared by the solid state reaction method. XRD patterns showed that the lattice structures were changed after polarization. The temperature dependence of the dielectric constant and dielectric loss, pyroelectric coefficient and DSC curves of LNN ceramics showed that there exist three phase transitions from room temperature up to the Curie temperature. The hysteresis loop and piezoelectric properties were measured and discussed.     

Investigation of dielectric and relaxor ferroelectric properties in Ba(Zr x Ti1−x )O3 ceramics

Barium zirconate titanate Ba(Zr _x Ti_1?x )O₃ (BZT x?=?0.1, 0.15, 0.2, 0.25) ceramics doped with Nb₂O₅ have been prepared by a traditional solid phase reaction. The temperature dependence of dielectric permittivity has been investigated. The results show that the phase transition temperature T _c is depressed and the diffuse phase transition behavior is enhanced with increasing Zr content. The Cole–Cole plot has been discussed and the cause of the deviation has been analyzed. The temperature dependence of inverse dielectric constants was investigated. A modified Curie–Weiss law can be used to describe the diffuseness of a phase transition, and diffusion factor increases with the Zr content.