High dielectric permittivity of SrBi2Nb2O9(SBN) added Bi2O3 and La2O3

In this paper, the structural and dielectric properties of SrBi₂Nb₂O₉ (SBN) as a function of Bi₂O₃ or La₂O₃ addition level in the radio (RF) and microwave frequencies were investigated. The SBN, were prepared by using a new procedure in the solid-state reaction method with the addition of 3; 5; 10 and 15 wt.% of Bi₂O₃ or La₂O_3. A single orthorhombic phase was formed after calcination at 900 °C for 2 h. The analysis by x-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a crystal structure (a?=?5.5129 Å, b?=?5.5183 Å and c?=?25.0819 Å; α?=?β?=?γ?=?90°). Scanning Electron Microscope (SEM) micrograph of the material shows globular morphologies (nearly spherical) of grains throughout the surface of the samples. The Curie temperature found for the undoped sample was about 400 °C, with additions of Bi³⁺, the temperature decreases and with additions of La³⁺ the Curie temperature increased significantly above 450 °C. In the measurements of the dielectric properties of SBN at room temperature, one observe that at 10 MHz the highest values of permittivity was observed for SBN5LaP (5%La₂O₃) with values of 116,71 and the lower loss (0.0057) was obtained for SBN15LaP (15%La₂O₃). In the microwave frequency region, Bi₂O₃ added samples have shown higher dielectric permittivity than La₂O₃ added samples, we highlight the SBN15BiG (15 % Bi₂O₃) with the highest dielectric permittivity of 70.32 (3.4 GHz). The dielectric permittivity values are in the range of 28–71 and dielectric losses are of the order of 10^?2. The samples were investigated for possible applications in RF and microwave components.     

Simultaneous preparation and densification of lead magnesium niobate-based ferroelectrics

Abstract

Ferroelectric lead titanate-doped lead magnesium niobate ceramics have been prepared and densified simultaneously by a new reaction sintering process. At low temperatures, the pyrochlore phase is firstly formed, which induces the expansion of the specimens. When the perovskite phase begins to produce at elevated temperatures, the specimens rapidly shrink, indicating the occurrence of reaction sintering. After sintering at 850°C, monophasic Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ solid solutions with high density are obtained. With an increase in the doping amount of PbTiO₃, the maximum dielectric permittivity and the Curie temperature increase; however, the relaxor characteristics of Pb(Mg_1/3Nb_2/3)O₃ become weakened. With the addition of 15 mol% PbTiO₃, the maximum dielectric permittivity is over 25000 at 1 kHz. It is concluded that monophasic and densified Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ with high dielectric permittivity are successfully prepared by the newly developed reaction sintering process.     

Electrical and mechanical properties of MgO added 0.5Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript>–0.5(Ba<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>)TiO<Subscript>3</Subscript> (BZT–0.5BCT) composite ceramics

MgO (0–2.0 vol%) added Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT-0.5BCT) ceramics have been prepared by the conventional solid-state reaction method. The effects of MgO powder on the phase formation, densification, dielectric, piezoelectric and mechanical properties (flexural strength, hardness) of the BZT-0.5BCT ceramics have been studied systematically. The synthesized powder could be densified to 97 % of true density at a temperature of 1350 °C. The MgO addition also provided materials with better mechanical properties. The most interesting aspect of MgO added samples is their relative permittivity vs. temperature response. MgO additions effectively suppress the relative permittivity around phase transition temperature. The aging rate of d₃₃ observed for BZT-0.5BCT is 14 %/decade. MgO addition reduces the ageing rate and for 1 vol% MgO added, BZT-0.5BCT shows aging rate of 3 %/decade. BZT-0.5BCT/MgO ceramics possesses good mechanical properties viz., flexural strength 93 MPa, which is almost 25 % higher than that of monolithic BZT-0.5BCT (73 MPa).     

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.     

DIELECTRIC BEHAVIOUR OF A NANOGRAIN PMN POWDERS

ABSTRACT

Dielectric permittivity of 150 nm mean grain size Pb(Mn_1/3Nb_2/3)O₃ (PMN) nanopowder has been investigated by dielectric spectroscopy in the 20 Hz–1 MHz frequency range and 100 K–400 K temperature range. The broad and diffused dielectric dispersion has been observed, but the dispersion region and the maximum of the real part of dielectric permittivity is shifted to lower temperatures compare to PMN single crystal and ceramics. The mean relaxation time, obtained from fits of the frequency dependences of the dielectric permittivity with Cole-Cole formula, changes according to the Vogel-Fulcher law with the freezing temperature T ₀ = 88 K which is much lower than in bulk PMN materials.     

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

Detection of micron size phantom of biological cell using concentric square ring metamaterial at microwave frequency

ABSTRACT

This paper presents simulation studies and theoretical analysis of sensing property of concentric square ring metamaterial biological materials. Phantom of dielectric cell having dimension 100 µm long and 25 µm in radius is considered. Sensor is designed using periodic arrays of split ring resonators and wires having negative permittivity and permeability at 16.694 GHz. Transmission parameters are extracted using CST MWS software. Change in resonance is observed on placing phantom close to the sensor due to the change in capacitance and inductance. Designed sensor can sense single phantom cell with 133 MHz of shift in resonance. Study shows that sensor has good sensitivity for detecting micron size dielectric objects.     

Enhanced dielectric properties of low-temperature-sintered Ba0.6Sr0.4TiO3 thick films

Ba_0.6Sr_0.4TiO₃ thick films were fabricated at a lower temperature of 880°C by adding Li₂O as sintering aid. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of films. After cold isostatic pressing prior to annealing, the thick film had a more compact morphology and better dielectric properties. The permittivity and tunability were increased to 1,318 and 19.04% from 925 and 14.81% while the dielectric loss was still kept low (1 MHz, 16 kV/cm). The enhanced properties and low-temperature sintering made BST thick films a potential candidate for Low Temperature Co-fired Ceramic (LTCC) and microwave tunable devices.     

Sintering and dielectric properties of (Ta2O5)1−x (TiO2) x polycrystalline ceramics

(Ta₂O₅)_1?x (TiO₂) _x system ceramics has been studied intensively as a promising dielectric material for next generation of high density dynamic random access memories instead of SiO₂ and Si₃N₄. It is found that the dielectric permittivity of (Ta₂O₅)_1?x (TiO₂) _x ceramics was dependent of fabrication process. But in the previous work, their calcining and sintering time were too long, generally for 24 h or even more. A relatively quick sintering process was provided which calcining and sintering time can be decreased to 12 h at 1200°C and 1 h at 1550°C, respectively. This kind of sintering process can save a lot of energy and time that is in favor of the industrial production. Under this sintering process, the composition dependent dielectric properties of (Ta₂O₅)_1?x (TiO₂) _x ceramics have been studied in a wide range of composition (0.01?≤?x?≤?0.20), and the dielectric constants of most compositions can be drastically enhanced. The maximum dielectric value can reach 216 at composition x?=?0.04. In the meantime, the mechanism of improvement of ceramic dielectric constants sintered at 1550°C was also discussed.     

High dielectric response of cobalt aluminate mullite (CAM) nanocomposite over cobalt aluminate mullite polymer (CAMP) nanocomposite in PVDF matrix

In this communication we have compared the dielectric behavior of cobalt aluminate mullite (CAM) nanocomposite and cobalt aluminate mullite polymer (CAMP) nanocomposite with different molar concentration of Co ⁺² ions. The study of dielectric property of the CAM samples as well as that of the CAMP samples at room temperature shows that at all concentrations the dielectric constant is higher than pure mullite and there is a critical concentration of Co ⁺², where maximum enhancement of dielectric property occurs. This paper demonstrates that the loading of a conductive component into a highly insulating matrix is an effective way to fabricate composites with high permittivity as well as a charge storage material. We have designed a device using CAM as the electrode material and CAMP as the separator to compare it with a commercial Li-polymer ion mobile battery. We observed that the charge storage ability of the composite system is better than the commercial Li-polymer ion mobile battery. Our device persists for more than 24 h while the maximum voltage recorded by the device is 0.885 V, whereas the maximum voltage recorded by the conventional commercial Li-polymer ion mobile battery is 0.566 V.     

Dielectric,impedance and modulus spectroscopy of BaBi2Nb2O9

Barium Bismuth Niobate (BaBi₂Nb₂O₉) has been synthesized by solid state reaction method. The X-ray diffraction study confirms the formation of compound. Morphological analysis has been carried out from the scanning electron microscopy images and the elemental analysis from the energy dispersive spectroscopy profiles. Investigation of dielectric and ferroelectric properties of the sample was done by varying the temperature from 25 °C - 500 °C in a frequency range of 1 kHz- 1 MHz. At 100 kHz, the phase transition was observed at 214.02°C. Further, this ferroelectric bi-layered perovskite exhibits an interesting relaxor behavior with a strong dispersion of the dielectric permittivity. A detailed study on the impedance spectroscopy over a wide range of temperature and frequency exhibits the contribution of grain ad grain boundary on different electrical parameters. From modulus spectroscopy, the presence of non-Debye type of relaxation in the material has been manifested. The complex modulus plots support the negative temperature coefficient of resistance (NTCR) type behavior of the material.     

A generalized arrhenius law in dilute KTaO3Li versus the Vogel-Fulcher approach

Abstract

The temperature-frequency dependencies (5 K-300 K, 100 Hz-1 MHz) of the dielectric permittivity ε′ and ε″ in dilute (x < 0.01) K_1-xLi_xTaO₃ were studied and analyzed in detail. From the positions of the permittivity temperature maxima at various frequencies it was obtained that the temperature dependence of the mean relaxation time of Li⁺ off-centre related 90° dipole reorientations doesn't obey an Arrhenius law, but follows the empirical Vogel-Fulcher law. Such behaviour is usually believed to be an evidence of freezing phenomenon and polar glass formation at low temperatures. Here we suggest an alternative explanation and show that taking into consideration the coupling of the Li⁺ dipole impurities to the soft mode allows to obtain an analytical expression for a “Generalized Arrhenius law”, which describes quantitatively the deviation from the Arrhenius law and agrees well with the experiment. The approach developed describes the dependence of the ′'(T) maxima too due to the hardening of the soft mode caused by random fields. This hardening suppresses the divergent dielectric permittivity at the ferroelectric-type phase transition and can possibly lead to the appearance of polar regions.     

Colossal dielectric permittivity of BaTiO3-based nanocrystalline ceramics sintered by spark plasma sintering

In pursuit of high permittivity materials for electronic application, there has been a considerable interest recently in the dielectric properties of various perovskite oxides like calcium copper titanate or lanthanum doped barium titanate. When processed in a particular way, this later material present at ambient temperature and at f?=?1 kHz unusual interesting dielectric properties, a so called “colossal” permittivity value up to several 10⁶ with relatively low dielectric losses. Moreover and contrary to what is classically expected and evidenced for this type of materials, no temperature dependence is observed. This behavior is observed in nanopowders based ceramics. An assumption to explain the observed properties is proposed. These results have important technological applications, since these nanoceramics open a new route to the fabrication of very thin dielectric films.     

Structure and Dielectric Properties of Heteroepitaxial PMNT Thin Films

Thin films of PbMg_1/3 Nb_2/3O₃(PMN) and (1 ? x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ (PMNT) with x = 0.1 to 0.3 were epitaxially grown on (100) MgO and (100) SrTiO₃ (ST) substrates by magnetron sputtering. Typical film thickness was 300 to 900 nm. Pyrochlore free (001) PMN and (001) PMNT thin films were grown on the ST and MgO substrates at narrow temperature window of 500 ± 20°C. The cross-sectional TEM image showed that the sputtered PMN and PMNT thin films comprised high density and continuous structure. These sputtered films showed 3-dimensional epitaxy. The dielectric response of the sputtered thin films showed frequency dispersion similar to bulk relaxor-like behavior with a broad temperature anomaly. PMN-23PT (x = 0.23) thin films showed the temperature of maximum, Tm, at 80°C. The Tm coincided with that of corresponding bulk materials. However, the obtained maximum dielectric permittivity, ?_m, ?_m = 900 to 1000, was considerably smaller than that in the bulk. The relatively low dielectric permittivity was probably due to the presence of strained hetero-epitaxial layer having temperature independent dielectric properties.     

Fabrication and properties of 2D EBGs by moulding/demoulding with high permittivity ceramics

Two-dimensional electromagnetic bandgap structures (2D EBGs) are designed and fabricated by moulding/demoulding. A high permittivity and low dielectric loss microwave material, Bi₂O₃-ZnO-Nb₂O₅ (BZN) was used. The impacts of high permittivity on the 2D EBGs’ properties are investigated. As the experiments showed, wide electromagnetic band gap is found in the frequency ranges from 5.6 to 10.6 GHz, and 12.6 to 16.6 GHz. The first gap is greater than 60% of the gap center frequency, while the second gap is 25% of the center frequency. The interval between the two gaps is larger than 2 GHz, and the return loss of both gaps is as large as ?40 dB. This interesting phenomenon of multi band gaps is very useful for diplexers, multi-mode tunable dielectric antennas and resonators. Based on these, expansive applications may be exploited in the future. The experimental results are in good agreement with the simulations’.     

Microstructure and electrical properties of the rare-earth doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 piezoelectric ceramics

Phase structure, microstructure, piezoelectric and dielectric properties of the 0.4 wt% Ce doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (Ce-BNT6BT) ceramics sintered at different temperatures have been investigated. The powder X-ray diffraction patterns showed that all of the Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The morphologies of inside and outside of the bulk indicated that the different sintering temperatures did not cause the second phase on the inside of bulk. However, the TiO₂ existed on the outside of the bulk due to the Bi₂O₃ and Na₂O volatilizing at higher temperature. The ceramics sintered at 1,200 °C showed a relatively large remnant polarization (P _r) of about 34.2 μC/cm², and a coercive field (E _c) of about 22.6 kV/cm at room temperature. The permittivity ? _r of the ceramics increased with the increasing of sintering temperature in antiferroelectric region, the depolarization temperature (T _d) increased below 1,160 °C then decreased at higher sintering temperature. The resistivity (ρ) of the Ce-BNT6BT ceramics increased linearly as the sintering temperature increased below 1,180 °C, but reduced as the sintering temperature increased further. A maximum value of the ρ was 3.125?×?10¹⁰ ohm m for the Ce-BNT6BT ceramics sintered at 1,180 °C at room temperature.     

Low-coercive PZT-based material possessing the properties of ferroelectric and relaxor

Abstract

The multicomponent rhombohedral ferroelectric PZT-based material with the impurity of a tetragonal phase, modified with certain additives was studied. Its Curie point is 215 °C. The peculiarities of microstructure, dielectric and pyroelectric properties, and also the dependence of the dielectric permittivity maximum temperature on the measuring field frequency suggest that this material belongs to ferroelectrics-relaxors.     

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.     

Dielectric Properties of Yttrium Vanadate Crystals from 15 K to 295 K

Yttrium Vanadate (YVO₄) is a birefringent crystal, which has similar dielectric constant as that of Sapphire. In this paper we have reported the measurement of the real part of permittivity and loss tangent of YVO₄ crystal in the temperature range 15–295 K at a frequency of 16.3 GHz. We have used the dielectric post resonator technique for the microwave characterisation of the YVO₄ dielectric rod. The multifrequency Transmission Mode Q-Factor (TMQF) technique has been used for data processing and hence precise values of permittivity and loss tangent are achieved. Easily machineable YVO₄ is characterized by low losses at microwave frequencies. At temperature of 15 K and frequency of 16.3 GHz the permittivity was 9.23 and loss tangent was 2 × 10^{− 5}. YVO₄ is identified as a potential candidate to replace expensive Sapphire in many microwave applications.     

Piezoelectric properties of the high temperature MPB xPbTiO3 - (1−x)[BiScO3 + Bi(Ni1/2Ti1/2)O3] composition

The ternary perovskite xPbTiO₃ - (1?x)[BiScO₃ + Bi(Ni_1/2Ti_1/2)O₃] (PT-BS-BNiT), where x?=?0.54 is the morphotropic phase boundary composition, was studied for high temperature ferroelectric applications. Polycrystalline ceramics were prepared using the standard solid-state methods. The stoichiometric ceramic was found to have room temperature dielectric permittivity and loss values at 1 kHz of 1490 and 0.049 respectively. Piezoelectric properties, of the stoichiometric composition, measured included: P_r?=?31.0 μC/cm², E_c?=?25.0 kV/cm, d₃₃?=?340 pC/N, d₃₃ ^*?=?896 pm/V, and a bipolar electromechanical strain of 0.25 %. From these data, the Curie temperature was T_C?=?370 °C and the depoling temperature was T_D?=?325 °C. Processing ceramics with excess bismuth improved the low field piezoelectric coefficients with a maximum of d33?=?445 pC/N, while increasing the lead content increased the transition temperatures. The depoling and Curie temperatures of all compositions were measured to be between 275 and 400 °C.