Structural and impedance properties of KBa2V5O15 ceramics

The polycrystalline sample of KBa₂V₅O₁₅ ceramics was prepared by a mixed oxide method at low temperature (i.e., at 560 °C). The formation of the compound was confirmed using an X-ray diffraction technique at room temperature. Scanning electron micrograph of the material showed uniform grain distribution on the surface of the sample. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 323 °C, and exhibits diffuse phase transition. Electrical properties of the material were analyzed using a complex impedance technique. The Nyquists plot showed the presence of both grain (>10³ Hz) and the grain boundary (<10³ Hz) effects in the material. Studies of electrical conductivity over a wide temperature range suggest that the compound exhibits the negative temperature coefficient of resistance behavior. The ac conductivity spectrum was found to obey Jonscher's universal power law.     

Ferroelectric phase transition in Ba4SrSmTi3V7O30 ceramics

Polycrystalline Ba₄SrSmTi₃V₇O₃₀ sample was prepared using high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the compound shows the formation of a single phase compound (orthorhombic crystal system) at room temperature. Microstructures of the compound exhibit uniform distribution of grains over the surface of the sample. Detailed studies of dielectric and electrical properties as a function of frequency (1 kHz to 1 MHz) and temperature (31 °C to 475 °C) show that, the compound exhibits a diffuse ferroelectric phase transition. Measurements of electrical conductivity (ac) as a function of temperature suggest that the compound has semiconducting properties much above the room temperature with a negative temperature coefficient of resistance behavior. The existence of ferroelectricity was confirmed from polarization studies.     

Structural and dielectric studies of Li2SiO3 ceramic

Lithium metasilicate (Li₂SiO₃) ceramic was prepared via solid-state reaction technique. X-ray diffraction pattern showed that Li₂SiO₃ ceramic is orthorhombic. Microstructural analysis by field emission scanning electron microscopy (FE-SEM) shows that the compound has well defined grains separated by grain boundaries. Dielectric studies of the compound shows a strong frequency dispersion of permittivity in the low frequency region followed by a nearly frequency independent behavior in the high frequency region. The dielectric permittivity and dielectric loss at 5 MHz are 25.66 and 0.033 at room temperature. The activation energy (E_a) of the sample calculated from the plot of ac conductivity versus inverse of absolute temperature was found to be less than 1 eV. The smaller activation energy of the compound within moderate temperature range suggests the presence of singly ionized oxygen vacancies in the conduction process.     

Structural and dielectric properties of parylene-VT4 thin films

58% semi-crystalline thin parylene-VT4 (–H₂C–C₆F₄–CH₂−)_n films, have been investigated by dielectric spectroscopy for temperature and frequency ranges of [−120 to 380 °C] and [0.1–10⁵ Hz] respectively. The study comprises a detailed investigation of the dielectric constant, dielectric loss and AC conductivity of this fluoropolymer. Dielectric behavior of parylene-VT4 is represented by a low dielectric constant with values in the range of 2.05–2.35 while the dielectric losses indicate the presence of two relaxation processes. Maxwell−Wagner−Sillars (MWS) polarization at the amorphous/crystalline interfaces with activation energy of 1.6 eV is due to the oligomer orientation. Electrical conductivity obeys to the well-known Jonscher law. The plateau in the low frequency part of this conductivity is temperature-dependent and follows an Arrhenius behavior with activation energy of 1.17 eV (deep traps) due to the fluorine diffusion. Due to its thermal stability with a high decomposition temperature (around 400 °C under air and 510 °C under nitrogen) and due to its good resistivity at low frequency (10¹⁵–10¹⁷ Ω m⁻¹), parylene-VT4 constitutes a very attractive polymer for microelectronic applications as low k dielectric. Moreover, when parylene-VT4 is subjected to an annealing, the dielectric properties can be still more improved.     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

Characteristics of high-k gate oxide prepared by oxidation of multi-layered Hf/Zr/Hf/Zr/Hf metal films

We investigated the physical and electrical properties of Hf-Zr mixed high-k oxide films obtained by the oxidation and annealing of multi-layered metal films (i.e., Hf/Zr/Hf/Zr/Hf, ∼ 5 nm). We demonstrated that the oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf-Zr mixed oxide film was formed on the top of silicate film due to inter-diffusion between Hf and Zr layer. This film shows the improved dielectric constant (k) and the raised crystallization temperature. Compared with HfO₂ and ZrO₂ gate dielectric, the crystallization temperature of Hf-Zr mixed oxides was raised by more than 200 °C. Using AES and XPS, we observed that Zr oxide has more fully oxidized stoichiometry than Hf oxide, irrespective of annealing temperatures. We also found that the thickness of an interfacial layer located between Hf-Zr mixed oxide and Si substrate also increases as annealing temperature increases. Especially, the thin SiO_x interfacial layer starts to form if annealing temperature increases over 700 °C, deteriorating the equivalent oxide thickness.     

Effect of copper-oxide segregation on the dielectric properties of CaCu3Ti4O12 thin films fabricated by pulsed-laser deposition

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO₂/SiO₂/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 °C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (∼ 20 °C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, ε_r, of CCTO thin films deposited at 750 °C with severe surface segregation (ε_r ∼ 750 at 10 kHz) was found to be much lower than that (ε_r ∼ 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries.     

Conductivity and dielectric studies on (Na0·4Ag0·6)2PbP2O7 compound

Electrical properties of the (Na_0·4Ag_0·6)₂PbP₂O₇ compound were studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range (484–593 K). Combined impedance and modulus plots were used to analyse the sample behaviour as a function of frequency at different temperatures. Temperature dependence of d.c. and a.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conduction activation energy was found to obey a mathematical formula.     

Synthesis and analysis of lead-free tungsten bronze ferroelectrics

The polycrystalline Ba₂Sr₃GdTi₃V₇O₃₀, a member of tungsten bronze structural family, was prepared by a solid-state reaction method at high temperature (calcination and sintering temperatures at 950 and 1,000 °C, respectively). Preliminary structural study showed that the compound has orthorhombic crystal structure at room temperature. Study of surface morphology of the compound by scanning electron microscopy exhibits the uniform grain distribution on the surface of the sample with less number of voids. The dielectric anomaly observed at 313 °C is considered as a ferroelectric-paraelectric phase transition temperature which has been confirmed by appearance of hysteresis loop at room temperature. The trend of variation of ac conductivity with inverse of absolute temperature provides the nature of conduction mechanism in the material. The different value of activation energy in different temperature regions suggests that the conduction process in the material is of mixed-type (i.e., ionic–polaronic and space charge due to the oxygen ion vacancies).     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

Deposition and dielectric properties of CaCu3Ti4O12 thin films deposited on Pt/Ti/SiO2/Si substrates using radio frequency magnetron sputtering

Polycrystalline CaCu₃Ti₄O₁₂ thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates using radio frequency magnetron sputtering. The phase formation and the physical quality of the films were crucially dependent on the substrate temperature and oxygen partial pressure. Good quality films were obtained at a substrate temperature of 650 °C and 4.86 Pa total pressure with 1% O₂. The dielectric constant (∼ 5000 at 1 kHz and 400 K) of these films was comparable to those obtained by the other techniques, eventhough, it was much lower than that of the parent polycrystalline ceramics. For a given temperature of measurements, dielectric relaxation frequency in thin film was found to be much lower than that observed in the bulk. Also, activation energy associated with the dielectric relaxation for the thin film (0.5 eV) was found to be much higher than that observed in the bulk ceramic (0.1 eV). Maxwell-Wagner relaxation model was used to explain the dielectric phenomena observed in CaCu₃Ti₄O₁₂ thin films and bulk ceramics.     

Dielectric properties of low temperature sintered LiF doped BaFe0.5Nb0.5O3

Sintering of BaFe_0.5Nb_0.5O₃:BFN requires the use of high temperatures to achieve satisfactory densification of this material. The aim of this study is to determine the effect of LiF on the sintering and electrical properties of BFN ceramics (the LiF was added as a sintering agent). The results show that LiF lowers the sintering temperature by 150-200 °C without affecting the formation of BFN. Ceramics doped with 2-3% LiF show optimum densities of about 93-94% of the theoretical value when sintered at low temperatures (1000-1100 °C). Samples containing 2-3% LiF show the following dielectric behaviour. The dielectric constant curves are very broad over a wide temperature range, with room-temperature values of 7154 in the 2% LiF sample and 2527 in the 3% LiF sample. The dielectric constants gradually increase up to 300 °C to values of about 38,862 in the 2% LiF sample and 40,471 in the 3% LiF sample. Furthermore, the addition of 2-3% LiF to BFN causes a reduction in the room-temperature dielectric loss from 4.29 in undoped BFN to less than 1.2 for LiF-containing samples.     

Dielectric relaxation in complex perovskite oxide In(Ni1/2Zr1/2)O3

The dielectric study of indium nickel zirconate, In(Ni_1/2Zr_1/2)O₃ (INZ) synthesized by solid state reaction technique is performed in a frequency range from 500 Hz to 1 MHz and in a temperature range from 303 to 493 K. The X-ray diffraction analysis shows that the compound is monoclinic. A relaxation is observed in the entire temperature range as a gradual decrease in ?′(ω) and as a broad peak in ?″(ω) in the frequency dependent real and imaginary parts of dielectric constant, respectively. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. The frequencies corresponding to the maxima of the imaginary electric modulus at various temperatures are found to obey an Arrhenius law with activation energy of 0.66 eV. The Cole-Cole model is used to study the dielectric relaxation of INZ. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependent conductivity spectra follow the universal power law.     

Ac conductivity, dielectric losses, permittivity behavior of BaxSr1?xFe0.8Co0.2O3?δ (x?=?0, 0.5 and 1) ceramics

In this paper, we have investigated ac conductivity, dielectric losses, permittivity of Ba _x Sr_1−x Fe_0.8Co_0.2O_3−δ (x = 0, 0.5, 1) ceramics. It has been observed that increase in barium content decreases activation energy (i.e. conductivity increases) in the higher temperature region (550–770 K). In the lower temperature region system with x = 0 shows metallic conductor behavior and system with x = 1 shows thermally activated behavior. The ferroelectric peak temperatures are observed at 700, 750 and 723 K for x = 0, 0.5 and 1, respectively. This peak temperature can be attributed to the oxygen-vacancy-related dielectric relaxation. With the increase of barium content the dielectric dispersion tend to diminishes. Partial substitution of strontium with barium (for x = 0.5) reduces dielectric losses by 50%.     

Dielectric and impedance properties’ studies of the of lead doped (PbO)-Co2Y type hexaferrite (Ba2Co2Fe12O22 (Co2Y))

In the present work, the preparation of a layered magnetic ceramic oxide Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) is described by the solid state reaction method. X-ray diffraction (XRD) technique was used to study the structural properties. The Rietveld refinement method has confirmed a hexagonal crystal structure with lattice parameters (a = b = 5.8560 ? and c = 43.4977 ?; α = β = 90° and γ = 120°). The dielectric and electrical modulus properties were studied over a range of frequency (1 Hz to 1 MHz) and temperature (313–493 K) using the complex impedance spectroscopy (CIS) technique. The impedance plot showed the first semicircle at high frequency which corresponds to grain effect and the second semicircle at lower frequency which corresponds to grain boundary (conduction phenomenon). A complex modulus spectrum was carried out in order to understand the mechanism of the electrical transport process, which indicates that a non-exponential type of conductivity relaxation is present in this material. The values of the activation energy of the compound (calculated both from dc conductivity and modulus spectrum) are very similar, and hence the relaxation process may be attributed to the same type of charge carriers. The study of the dielectric property, conductivity and loss of ferrite materials, as a function of temperature, is important for microwave absorption applications. The protection of sensitive circuits from the interference of external microwave radiation, is an important technological application of these materials.     

Structural and electrical characteristics of Sr(Fe2/3W1/3)O3 ceramics

The polycrystalline samples of Sr(Fe_2/3W_1/3)O₃ (SFW) were prepared by a high-energy ball-milling followed by solid-state reaction technique. The X-ray structural analysis showed the formation of single-phase compound in the tetragonal system, which is a distorted structure of an ideal cubic perovskite. The temperature–frequency dependence of dielectric constant and loss tangent exhibited relaxation behavior of the compound. The studies of impedance parameters (Z′, Z″) as a function of temperature and frequency have confirmed the contribution of bulk resistance of SFW. The small value of activation energy of the compound (～ 0.35 eV) can be explained by mixed ionic–polaronic conductivity mechanism.     

Preparation,phase structure and microwave dielectric properties of a new low cost MgLi2/3Ti4/3O4 compound

A novel Li-based spinel compound with the composition of MgLi_2/3Ti_4/3O₄ was synthesized by the conventional solid-state reaction method. The phase structure was studied by X-ray diffraction (XRD) technique. When the calcination temperature was over 1050 °C, a single phase compound which has a cubic structure [Fd-3m (227)] with cell parameters of a = 8.4057 Å, V = 593.91 Å³, ρ = 3.51 g cm⁻³ and Z = 8 was obtained. MgLi_2/3Ti_4/3O₄ ceramic could be well densified after sintering above 1125 °C. The microwave dielectric properties were measured using a microwave vector network analyzer in the frequency range of 7–9 GHz MgLi_2/3Ti_4/3O₄ ceramic sintered at 1125 °C for 2 h showed microwave dielectric properties of ?_r = 20.2, Q × f = 62,300 GHz, and τ_f = −27.1 ppm °C⁻¹. Furthermore, 0.95MgLi_2/3Ti_4/3O₄–0.05CaTiO₃ ceramic sintered at 1200 °C for 2 h exhibited good properties of ?_r = 22.6, Q × f = 48,000 GHz, and τ_f = −2.3 ppm °C⁻¹.     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

Dielectric and modulus studies of LiNiPO4

Olivine-structured LiNiPO₄ has been prepared by a Pechini-type polymerizable precursor method. The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman Spectroscopy techniques, respectively. Brunauer, Emmett and Teller surface area (BET) of the compound also studied. LiNiPO₄ has orthorhombic structure whose dielectric and modulus properties are studied over the frequency range of 1 MHz to 10 Hz at different temperatures (150–300 °C) using impedance spectroscopy. The frequency and temperature dependence of dielectric permittivity, dielectric loss and electric modulus of LiNiPO₄ are studied. The frequency dependent plot of modulus show that the conductivity relaxation is of non-Debye type.     

Effects of Bi2O3 and Cr2Ti3O9 Co-doping on dielectric properties in BaTiO3-based ceramics

A microwave ceramic with general composition (1-x-y) BaTiO₃ + x Cr₂Ti₃O₉ + y Bi₂O₃ has been prepared by solid state synthesis at 1300-1400 °C. The phase composition, perovskite structural parameters and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. At low doping levels the formation of BaTiO₃-based solid solution has been found. The precipitation of BaCrO₃ has been detected at x = y = 2.0 mol%. A model of the incorporation of Cr³⁺ and Bi³⁺ ions into BaTiO₃-based crystal lattice has been proposed. Diffused phase transition in the temperature range 100-140 °C have been revealed by dielectric measurements for different ceramic composition. As high dielectric constant as 7311 and as low dielectric loss as 0.02 have been found for the composition of 0.98BaTiO₃-0.01Cr₂Ti₃O₉-0.01Bi₂O₃.