Dielectric properties of iron doped calcium copper titanate, CaCu2.9Fe0.1Ti4O12

CaCu_2.9Fe_0.1Ti₄O₁₂ (CCFTO) has been prepared by a novel semi-wet route and its dielectric properties have been studied in the temperature range 300-500 K. It is found that dielectric constant (?) decreases drastically in the frequency range 100 Hz to 1 MHz. Complex plane impedance and modulus analysis was done to understand this drastic decrease in ?. Oxidation state of various ions was studied using X-ray photoelectron spectroscopy (XPS). The decrease in the permittivity of CCFTO can be attributed to two factors: the suppression of the Ca/Cu disorder in CCFTO which is observed in CaCu₃Ti₄O₁₂ (CCTO) and the absence of the grain boundary internal barrier layer capacitance mechanism.     

Crystal structure and dielectric properties of La(Mg0.5Ti0.5)O3-Ca0.8Sm0.4/3TiO3 solid solution system at microwave frequencies

The crystal structure and the dielectric properties of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ ceramics have been investigated. Ca_0.8Sm_0.4/3TiO₃ was employed as a τ_f compensator and was added to La(Mg_0.5Ti_0.5)O₃ to achieve a temperature-stable material. The formation of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ solid solutions were confirmed by the XRD results and the measured lattice parameters for all compositions. The dielectric properties are strongly correlated to the sintering temperature and the compositional ratio of the specimens. Although the ?_r of the specimen could be boosted by increasing the amount of Ca_0.8Sm_0.4/3TiO₃, it would instead render a decrease in the Q × f. The τ_f value is strongly correlated to the compositions and can be controlled by the existing phases. A new microwave dielectric material 0.45La(Mg_0.5Ti_0.5)O₃-0.55Ca_0.8Sm_0.4/3TiO₃, possessing a fine combination of microwave dielectric properties with an ?_r of 47.83, a Q × f of 26,500 GHz (at 6.2 GHz) and a τ_f of −1.7 ppm/°C, is proposed as a very promising candidate material for today's 3G applications.     

High frequency response to the impedance complex properties of Nb-doped CaCu3Ti4O12 electroceramics

Impedance analyses was performed on undoped and Nb-doped CaCu₃Ti₄O₁₂ (CaCu₃Ti_4−xNb_xO_12+x/2; x = 0, 0.01, 0.03, 0.05, 0.1) to investigate their electrical properties. The pellet samples were prepared using the solid state reaction method. Silver electrode was deposited on both pellets’ surfaces for electrical measurement. The thermally etched samples showed tiny bumped domains within the grains. The existence of both domain and grain boundaries are believed to strongly influence the dielectric constant of CaCu₃Ti₄O₁₂ (CCTO). Undoped CCTO showed two arcs of impedance complex plane while Nb-doped samples have three arcs. Each arc represents the constituent elements of the CCTO. The highest frequency arc is evidence that CCTO consists of conductive domains which measure about 1 Ω and are insulated by two types of barriers, i.e. domain boundary and grain boundary.     

Origin of giant dielectric constant in Ba[(Fe1−xCox)1/2Nb1/2]O3

The X-ray diffraction Rietveld refinement of Ba[(Fe_1−xCo_x)_1/2Nb_1/2]O₃ with 0 ≤ X ≤ 1 shows cubic structure formation with space group P_m3_m. No distinct tilting of oxygen octahedron is observed. The dielectric measurement of such a cubic system exhibited giant values (?′ > 10⁴) in the temperature range of 298-483 K and frequency range of 10²-10⁵ Hz. An analysis of the permittivity, electric modulus, and electrical conductivity properties in these systems confirmed the presence of oxygen vacancies induced dipolar relaxation. Our investigations show that the observed extremely high dielectric constant values are predominantly the result of oxygen vacancies induced dipoles produced at the grain boundaries. Additional significant intrinsic contributions to the permittivity comes from the directly doped electrons at the unit cell, as indicated by the enhancement in the observed values of the permittivity on replacement of Fe³⁺ (3d⁵) by Co³⁺ (3d⁶). The contributions of the doped free charges and the oxygen vacancy induced dipoles are separated using the Jump Relaxation Model.     

High-dielectric-constant and low-loss microwave dielectric in the (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 solid solution system

The microwave dielectric properties and microstructures of (1 − x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr_0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr_0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of −4.7 ppm/°C.     

Dielectric properties and crystal structure of La(Mg1/2Ti1/2)O3 ceramics with Mg substituted by Co

Solid solutions of (1 − x)La(Co_1/2Ti_1/2)O₃-xLa(Mg_1/2Ti_1/2)O₃ were used to prepare La(Mg_1−xCo_x)_1/2Ti_1/2O₃ using solid-state synthesis. X-ray diffraction patterns of the sintered samples revealed single phase formation. A maximum density of 6.01 g/cm³ was obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ (x = 1) ceramics sintered at 1375 °C for 4 h. The maximum values of the dielectric constant (?_r = 29.13) and the quality factor (Q × f = 80,000 GHz) were obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ with 1 wt% ZnO additive sintered at 1375 °C for 4 h. The temperature coefficient of resonant frequency τ_f was −59 ppm/°C for x = 0.3.     

Synthesis of (Bi0.5Na0.5)TiO3 (BNT) and Pr doped BNT using the soft combustion technique and its properties

In this work, bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT) and praseodymium (Pr)-doped BNT were successfully produced using the soft combustion technique. The effects of Pr doping on stoichiometry, microstructure, density and dielectric properties were studied. Pure Pr-doped BNT was obtained in all samples containing 5, 10 and 20 mol% Pr after calcination at 800 °C for 3 h. The produced powders were then pressed into pellets and sintered at 1100 °C for 3 h. The very similar ionic radii of Pr³⁺ with Bi³⁺ and Na⁺ made it possible to substitute both Bi and Na. The crystallite size and grain size decreased with increasing Pr amount because Pr acted as grain growth inhibitor, both for calcined powders and for sintered pellets. Maximum density was obtained in 5 mol% Pr-doped BNT, beyond which density decreased. The maximum dielectric constant of 756 was obtained in 5 mol% Pr-doped BNT and decreased at higher levels of Pr doping. Pr doped into BNT also caused a decrease in dielectric loss.     

Impedance analysis of thermally modified SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)₂O₉ (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. The obtained samples were thermally modified in high vacuum to study the influence of the formed defects on the dielectric and electrical properties of the samples. Scanning electron microscopy with an energy dispersion X-ray spectrometer was applied to investigate the grain structure and stoichiometry of the studied ceramics. Their dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material which was controlled by thermal modification of the tested ceramics. This phenomenon can be ascribed to the presence of ionized space charge carriers such as oxygen and bismuth vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. Moreover the temperature dependence of various electrical properties was determined and discussed.     

Effect of CaTiO3 addition on microwave dielectric properties of Mg2(Ti0.95Sn0.05)O4 ceramics

The microwave dielectric properties of CaTiO₃-added Mg₂(Ti_0.95Sn_0.05)O₄ ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg₂(Ti_0.95Sn_0.05)O₄ and perovskite-structured CaTiO₃ forms a two-phase system (1 − x)Mg₂(Ti_0.95Sn_0.05)O₄-xCaTiO₃, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ_f. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg₂(Ti_0.95Sn_0.05)O₄-0.09CaTiO₃ is suggested and it possesses a good combination of dielectric properties with an ?_r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ_f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.     

Dense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization

This paper presents the sintering behaviour of a La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 °C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 μm) favours a good sintering behaviour: open porosity disappear at 1400 °C and relative densities over 99% can be achieved after 6 h at 1450 °C. The same powder can also be sintered into a thin disc of ∼100 μm thickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 °C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 °C is ∼0.11 S cm⁻¹. Special attention is devoted to the temperature range between 200 °C and 400 °C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 °C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material.     

Impedance and modulus analysis of the (Na0.6Ag0.4)2PbP2O7 compound

The electrical properties of the (Na_0.6Ag_0.4)₂PbP₂O₇ compound were studied using the complex impedance spectroscopy in the temperature range (502-667 K). Grain interior, grain boundary and electrode-material interface contributions to the electrical response are identified by the analysis of complex plan diagrams. The imaginary part of the modulus at several temperatures shows a double relaxation peaks, furthermore suggesting the presence of grains and grain boundaries in the sample. An analysis of the dielectric constants ?′, ?″ and loss tangent tan(δ) with frequency shows a distribution of relaxation times. The dc conductivity of the material is thermally activated with an activation energy about 0.8 eV which is in the vicinity of the that obtained from tan(δ) (E = 0.7 eV) and modulus (E_m = 0.68 eV) studies.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

Correlating phase and microstructure development versus dielectric properties in La and Er co-doped Bi4Ti3O12 ferroelectric ceramics

Bi_3.25La_0.75−xEr_xTi₃O₁₂ and Bi_3.25La_0.75Ti_3−xEr_xO_12−δ ceramics were prepared and studied in this work in terms of dopant-induced phase and microstructure development as well as dielectric response. The results show that introduction of Er³⁺ tends to reduce the materials’ sintering temperature and average grain size. Moreover, it was noted that in these systems the substitution site of this dopant is controlled by valence state and ionic radii mismatch effects. In particular, even when a nominal substitution of Ti⁴⁺ is conceived, here it is found that Er³⁺ also incorporates at the (Bi,La)³⁺ sites. These and other interesting concluding remarks from this work, including Er³⁺ tolerance, were possible only after comparing, especially, the X-ray diffraction results and the intrinsic ferroelectric characteristics extracted from the dielectric measurements.     

Effects of raw materials on microstructure and dielectric properties of PbZrO3 antiferroelectric thin films prepared via sol-gel process

In this work, we report on two kinds of PbZrO₃ (PZO) antiferroelectric (AFE) thin films with a thickness of about 700 nm, which were fabricated by using zirconium isopropoxide and zirconium nitrate as starting materials, respectively. The effects of the raw materials on microstructure and electrical properties of the PZO AFE films were studied in detail. X-ray diffraction and scanning electron microcopy results showed that the PZO films obtained from zirconium isopropoxide were highly (1 1 1)-oriented and had a more uniform surface microstructure. As a result, the PZO films from zirconium isopropoxide accordingly displayed better electrical properties, such as lager dielectric constant, increased saturated polarization, and smaller leakage current.     

Influence of A-site Gd doping on the microstructure and dielectric properties of Ba(Zr0.1Ti0.9)O3 ceramics

Pure and Gd-doped barium zirconate titanate (BaZr_0.1Ti_0.9O₃, BZT) ceramics were prepared by solid state reaction method. Phase analysis showed the formation of the pyrochlore phase (Gd₂Ti₂O₇) at about 5 mol% Gd doping in BZT. The microstructural investigation on the sintered ceramics showed that Gd doping significantly reduced the grain size of pure BZT ceramics, from about 100 μm to 2-5 μm. Change in the Gd concentration had minor influence on the grain size and on morphology. An increase in the Gd content decreased the Curie temperature (T_C) of the BZT ceramics. The maximum dielectric constant at T_C was observed for 2 mol% Gd and with further increase in Gd content the dielectric constant at T_C decreased. The dielectric constant was significantly improved compared to that of pure BZT ceramic. Tunable dielectric materials with good dielectric properties can be prepared by doping BZT with Gd.     

Stress and defect induced enhanced low field magnetoresistance and dielectric constant in La0.7Sr0.3MnO3 thin films

Colossal magnetoresistive manganite La_0.7Sr_0.3MnO₃ (LSMO) films were prepared by pulsed laser deposition on three different single crystal substrates using different deposition parameters. Characterizations of their surface morphologies, structural, magnetic and magneto-transport properties show that films on MgO single crystal substrates contain higher amount of structural defects compared to those on SrTiO₃ (STO) and NdGaO₃ (NGO) substrates. Low deposition rate and thicker films give rise to polycrystallinity and grain boundaries. The films on MgO substrate showed a broad paramagnetic (PM) to ferromagnetic (FM) transition accompanied with metal-insulator transition (MIT) much below their Curie temperature (T_C) indicating growth of strained structures due to large lattice mismatch (9%) between the substrate and the film. The deposited films on STO and NGO show least effect of substrate induced strain exhibiting sharper PM-FM transition and metallic behavior below T_C. The magnetoresistance (MR) measured with 300 mT field clearly shows two contributions, one due to grain boundary tunneling and the other due to colossal MR effect. The highest low field MR effect of 17% was achieved for the film on MgO with the highest thickness and surface roughness indicating the presence of grain boundary related defects. Also a high dielectric constant was observed for the same film at room temperature up to 100 kHz frequency. Coexistence of defect induced large low-field MR and abnormally high dielectric constant can give rise to different exciting applications.     

Microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric resonators

Ba(Zn_1/3Ta_2/3)O₃ (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO₃, ZnO, and Ta₂O₅ powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications.     

Morphology and structure of LiNb0.6Ti0.5O3 particles by molten salt synthesis

M-phase LiNb_0.6Ti_0.5O₃ (LNT) plate-like particles with large anisometric shape were firstly fabricated by molten salt synthesis (MSS) method in LiCl flux. Effects of reaction temperature, holding time and the weight ratio of LiCl salt to the original powders on the phase structure and morphology of the synthesized particles were investigated. The LiNb_0.6Ti_0.5O₃ powders generally showed a multi-layer structure, exhibiting irregular hexagonal or triangle morphology. The reaction temperature showed a strong influence on the particle growth process, and pure LNT particles are obtained at 950 °C. Further increasing the reaction temperature and holding time could increase the average size of the particles. It revealed that the thickness of the plat-like particles was increased as the contents of the chloride salts increased. The synthesis process, the relation between crystal structure and morphology of particles were also discussed.     

New dielectric material system of La(Mg1/2Ti1/2)O3–Ca0.6La0.8/3TiO3 for microwave applications

The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. 0.6La(Mg_1/2Ti_1/2)O₃–0.4Ca_0.6La_0.8/3TiO₃ ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (_r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Properties of praseodymium-doped bismuth potassium titanate (Bi0.5K0.5TiO3) synthesised using the soft combustion technique

Bismuth potassium titanate (Bi_0.5K_0.5TiO₃; BKT) and praseodymium-doped BKT (Bi_0.5(1−x)Pr_xK_0.5TiO₃; BPKT) powders were synthesised using the soft combustion technique. Fine particles of 10-100 nm of BKT and BPKT were produced. A single phase BKT was obtained with a minimum of 0.5 mol of glycine. Various compounds of Bi_0.5(1−x)Pr_xK_0.5TiO₃ where x = 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20 were prepared. Pure BKT and BPKT powders were obtained after calcination at 800 °C for 3 h. After sintering at 1050 °C for 5 h, pure BKT and BPKT pellets were obtained for x = 0 and 0.01. However, for BPKT with x = 0.03, 0.05, 0.10, 0.15 and 0.20, a minor amount of Bi₄Ti₃O₁₂ (BIT) secondary phase was present after sintering at 1050 °C for 5 h. The crystallite size and grain size of all the samples followed similar trends, first increasing from x = 0 (undoped BKT) to x = 0.05 and then decreasing above x = 0.05. Among the undoped and doped samples, BPKT with x = 0.05 had the highest dielectric properties (?_r = 713.87) due to its large crystallite size (68.66 nm), large grain size (∼435 nm) and high relative density (93.39%).