Influence of Sm substitution on the phase,microstructure and microwave dielectric properties of SrLa<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript>

New dielectric ceramics in the SrLa_4−xSm_xTi₅O₁₇ (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route to investigate the effect of Sm⁺³ substitution for La⁺³ on the phase, microstructure and microwave dielectric properties. At x = 0–3, all the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1500–1580 °C. At x = 4, a mixture of Sm₂Ti₂O₇ and SrTiO₃ formed. The maximum Sm⁺³-containing single phase ceramics, SrLaSm₃Ti₅O₁₇, exhibited relative permittivity (ε_r) = 42.6, temperature coefficient of resonant frequency (τ _f ) = −96 ppm/^oC and quality factor (Q _u f _o ) = 7332 GHz. An analysis of results presented here indicates that SrLa_4−xSm_xTi₅O₁₇ ceramics, exhibiting τ _f  ~ 0 and ε_r ~ 53 could be achieved at x ~ 1.4 but at the cost of decrease in Q _u f _o .     

Influence of ZrO<Subscript>2</Subscript> addition on the structure,thermal stability,and dielectric properties of ZnTiO<Subscript>3</Subscript> ceramics

The zinc titanates doped with zirconium were synthesized by conventional solid-state reaction using metal oxides. X-ray diffractometry and differential scanning calorimetry analysis results indicated that the stable region of the hexagonal Zn(Zr _x Ti_1−x )O₃ phase extended to a high temperature (above 945 °C). The c/a value decreased as the Zr concentrations increased, which may be caused by the Zr⁴⁺ addition resulting in a shorter distance between the center ion and its nearest neighbors of the octahedron, and the bonding force between the B-site ion and oxygen ion of ABO₃ perovskite-like structure becoming stronger. The dielectric properties exhibited a significant dependence on the sintering temperatures and the amount of ZrO₂ addition. The dielectric constant decreased and Curie temperature (T _c) increased slightly with the increasing amounts of Zr ions. This is caused by the second phase of ZnZrO₃ which was deposited at the grain boundaries and inhibited the grain growth. Furthermore, diffuse phase transition with a maximum permittivity at a transition temperature that is close to room temperature in Zn(Zr _x Ti_1−x )O₃ was observed.     

Structural investigation and giant dielectric response of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca_0.95Nd_0.05Cu₃Ti_4?xZr_xO₁₂ (x?=?0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr⁴⁺ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (ε′ ~?16,902) and minimal tanδ (≤?0.10) over a wide frequency range. The giant ε′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr⁴⁺ ions at Ti⁴⁺ site.     

Synthesis,microstructure and microwave dielectric properties of Ca<Subscript>4-x</Subscript>Mg<Subscript>x</Subscript>La<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript> ceramics

Ca_4-xMg_xLa₂Ti₅O₁₇ ceramics were prepared by a solid state ceramic route for x = 0, 0.5, 1, 2, 3 and 4. The structure and microstructure of the ceramics were investigated using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. X-ray diffraction results show that the Ca_4-x Mg _x La₂Ti₅O₁₇ adopts an orthorhombic crystal structure with no secondary phase observed for x from 0 to 0.5. Secondary phase, MgTiO₃ occurs with further increasing doping level (1 ≤ x ≤ 3). When x = 4, mixture phases La_0.66TiO_2.993, MgTiO₃ and a trace of unknown phase coexist. Ca₄La₂Ti₅O₁₇ ceramic exhibits a relative permittivity (ε_r) ~ 65, quality factor (Q × f) ~13,338 GHz (at ~4.75 GHz), and temperature coefficient of resonant frequency (τ _f ) ~ 165 ppm/°C. The sintering temperature was distinctly reduced from 1,580 °C for x = 0 to 1,350 °C for x = 4. With increasing Mg content, ε_r and τ_f obviously decrease, while Q × f value initially decreases and then increases. The ceramic for x = 2 shows ε_r ~ 50, Q × f ~ 9,451 and τ _f  ~ 62.5 ppm/°C. By the complete replacement of Ca with Mg, Mg₄La₂Ti₅O₁₇ ceramic sintered at 1,350 °C for 4 h combines a high dielectric permittivity (ε _r  = 31), high quality factor (Q × f ~ 15,021) and near-zero temperature coefficient of resonant frequency (τ _f  ~ 4.0 ppm/°C). The materials are suitable for microwave applications.     

Effects of Nd-substitution on microstructures and dielectric characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Ca_1−3x/2Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2) ceramics were prepared by a solid state reaction process, and single-phased structures were obtained for all the compositions. The dielectric characteristics of pure and Nd-substituted CaCu₃Ti₄O₁₂ ceramics were investigated together with the microstructures. The mixed-valent structures of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in the present ceramics were confirmed by X-ray photoelectron analysis. The dielectric relaxation in the low temperature range was examined in detail and the variation of dielectric constant and dielectric loss was attributed to the modification mixed-valent structures.     

Properties of neodymium-doped Ca<Subscript>0.15</Subscript>Sr<Subscript>1.85</Subscript>Bi<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>18</Subscript> ferroelectric ceramics

Bismuth-layered compound Ca_0.15Sr_1.85Bi_4−xNd_xTi₅O₁₈ (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd³⁺ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics increases at beginning then decreases with increasing of Nd³⁺ doping level, and a maximum Pr value of 9.6 μC/cm² at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd³⁺ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (ε_r) and dielectric loss tangent (tan δ). The magnitudes of ε_r and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively.     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Studies on the relaxor behavior of sol-gel derived Ba(Zr x Ti1− x )O3 (0.30≤x≤0.70) thin films

We have studied the relaxor behavior of sol-gel derived Ba(Zr _x Ti_{1− x} )O₃ (0.30≤ x≤0.70) thin films. The plausible mechanism of the relaxor behavior has been analyzed from the dielectric data and micro-Raman spectra. Substitution of Zr⁺⁴ for Ti⁺⁴ in BaTiO₃ lattice reduces its long-range polarization order yielding a diffused paraelectric to ferroelectric phase transition. The solid solution system is visualized as a mixture of Ti⁺⁴ rich polar region and Zr⁺⁴ rich regions and with the increase in Zr contents the volume fraction of the polar regions are progressively reduced. At about 25.0 at% Zr contents the polar regions exhibit typical relaxor behavior. The degree of relaxation increases with Zr content and maximizes at 40.0 at% Zr doped film. The frequency dependence of the polar regions follows Vogel-Fulcher relation with a characteristic cooperative freezing at freezing temperature (T _f). Below T_f, a long range polarization ordering was ascertained from the polarization hysteresis measurement.     

Effects of dc bias on dielectric relaxations in CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Effects of dc bias on dielectric relaxations in CaCu₃Ti₄O₁₂ ceramics were investigated via an improved dielectric spectroscopy. A new low-frequency dielectric relaxation, which was assigned to space charge polarization, was found shifting towards higher frequency with increasing bias voltage in the improved spectra. It was suggested that the Schottky barrier at grain boundary was lowered under dc bias resulting in higher possibility for carriers to migrate. Therefore, the relaxation time was decreased, which was in accordance with rightward shift of this relaxation under increased dc bias. In addition, dependence of the widely reported high-frequency relaxation (>?10⁵ Hz) and middle-frequency relaxation (10³–10⁵ Hz) on bias voltage was also discussed. Permittivity contributed by either high-frequency or middle-frequency relaxation presented inverse dependence on dc bias. Discrepancy on barrier parameters was obtained assuming both of them physically correlated with the barrier at grain boundary.     

Phase, microstructure and microwave dielectric properties of Zr-doped SrLa4Ti5?xZrxO17

The effect of Zr⁺⁴ substitution for Ti⁺⁴ on the phase, microstructure and microwave dielectric properties of compositions in the SrLa₄Ti_5−xZr_xO₁₇ (0 ≤ x ≤ 0.1) series was investigated. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffractometer when sintered in the temperature range 1,450–1,580 °C for 4 h in air. The substitution of Zr⁺⁴ for Ti⁺⁴ enabled processing of highly dense ceramics with a decrease in temperature coefficient of resonant frequency (τ_f) from ~117 to 70 ppm/°C, dielectric constant (ε_r) from 60.8 to 57.3, with no significant effect on the quality factor. In the present study, optimum properties i.e. ε_r ~ 57.3, τ_f ~ 70 ppm/°C and quality factor (Q _u  × f _o ) ~ 9,841 GHz, were achieved for SrLa₄Ti_4.9Zr_0.1O₁₇. The trend of the results demonstrates that further studies with increased Zr⁺⁴ content are required to achieve ultra low loss SrLa₄Ti_5−xZr_xO₁₇ ceramics.     

Dielectric properties and relaxation of Bi<Subscript>0·5</Subscript>Na<Subscript>0·5</Subscript>TiO<Subscript>3</Subscript>-BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free ceramics

A new member of lead-free piezoelectric ceramics of the BNT-based group, (1 − x)Bi_0·5Na_0·5TiO_3−x BaNb₂O₆, was prepared by conventional solid state reaction and its dielectric properties and relaxation was investigated. X-ray diffraction showed that BaNb2O6 diffused into the lattice of Bi_0·5Na_0·5TiO₃ to form a solid solution with perovskite-type structure. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. The temperature dependence of dielectric constant at different frequencies revealed that the solid solution exhibited relaxor characteristics different from classic relaxor ferroelectrics. The samples with x = 0·002 and 0·006 exhibited obvious relaxor characteristics near the low temperature dielectric abnormal peak, T _f, and the samples with x = 0·010 and 0·014 exhibited obvious relaxor characteristics between room temperature and T _f. The mechanism of relaxor behaviour was also discussed according to the macro-domain to micro-domain transition theory.     

Structural,dielectric and impedance spectroscopy studies of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)(Zr<Subscript>0.025</Subscript>Ti<Subscript>0.975</Subscript>)O<Subscript>3</Subscript> ceramic

Structural, vibrational, dielectric and electrical properties of (Na_0.5Bi_0.5)(Zr_0.025Ti_0.975)O₃ ceramic synthesized by the solid-state reaction technique have been carried out. The X-ray diffraction analysis was indicated as a pure perovskite phase in the rhombohedral structure. The modes of rhombohedral vibrations were appeared in the experimental Raman spectrum at room temperature. The dielectric and electrical properties of the material were investigated by impedance spectroscopy analysis for a broad range of temperatures (50–560 °C) and frequency domain of 10²?10⁶ Hz. The dielectric measurement exhibit two phase transitions: a ferro-antiferroelectric transition followed by an antiferro-paraelectric transition at higher temperatures. Complex impedance analysis was carried out in order to distinct the contribution of the grains and the grain boundaries to the total electrical conduction. The Nyquist plot was proved to be a non-Debye relaxation mechanism. The combined spectroscopic plots of the imaginary part of electric impedance and modulus confirmed the non-Debye type behavior. The frequency dependent ac conductivity obeys the double power law behavior and shows three types of conduction process. The significant decrease of dc conductivity spectrum followed the Arrhenius relationship. The values of calculated activation energy of the compound implied that the electrical conduction is mostly due the high oxygen mobility.     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Studies on the dielectric and relaxor behavior of sol-gel derived barium strontium zirconate titanate thin films

The dielectric behavior of sol-gel derived Ba_0.80Sr_0.20(Zr_xTi_1−x)O₃ (0.0 ≤ x ≤ 0.50) thin films is studied. A relaxor behavior is observed for x ≥ 0.35. The degree of relaxation increases with Zr content. The frequency dependence of the polar regions follows Vogel-Fulcher relation with a characteristic cooperative freezing at freezing temperature (T_f). Below T_f, a long range polarization ordering is likely to take place. The plausible mechanism of the relaxor behavior of BSZT thin films with Zr contents ≥ 0.35 has been proposed based on the measured temperature as well as frequency dependent dielectric data. The solid solution system is visualized as a mixture of Ti^+ 4 rich polar regions and Zr^+ 4 rich regions; with the increase in Zr content the volume fraction of the polar regions is progressively reduced. At and above 35.0 at.% Zr substitution the polar regions exhibit typical relaxor behavior.     

Microwave dielectric properties and its compatibility with silver electrode of LiNb<Subscript>0.6</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript> with B<Subscript>2</Subscript>O<Subscript>3</Subscript> and CuO additions

The influences of B₂O₃ and CuO (BCu, B₂O₃: CuO = 1:1) additions on the sintering behavior and microwave dielectric properties of LiNb_0.6Ti_0.5O₃ (LNT) ceramics were investigated. LNT ceramics were prepared with conventional solid-state method and sintered at temperatures about 1,100 °C. The sintering temperature of LNT ceramics with BCu addition could be effectively reduced to 900 °C due to the liquid phase effects resulting from the additives. The addition of BCu does not induce much degradation in the microwave dielectric properties. Typically, the excellent microwave dielectric properties of ε_r = 66, Q × f = 6,210 GHz, and τ _f  = 25 ppm/^oC were obtained for the 2 wt% BCu-doped sample sintered at 900 °C. Chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Enhancing the microwave dielectric properties of Sr<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Ta<Subscript>4</Subscript>TiO<Subscript>17</Subscript> ceramics by Zr Substitution

The compositions in Sr₂Ca₃Ta₄Ti_1?xZr_xO₁₇ (0?≤?x?≤?0.12) series were designed and fabricated by solid state sintering method. All the compositions formed single phases and crystallized in an orthorhombic crystal structure. Zr substitution led to the enhancing of the microwave dielectric properties by tuning the τ_f value through zero and increased the Q_uf_o value from 12,540 to 14,970 GHz with a slight decrease in ε_r. In the present study, a good combination of ε_r ~?51, Q_uf_o ~?145,43 GHz and τ_f ~ 3 ppm/°C were obtained for Sr₂Ca₃Ta₄Ti_0.90Zr_0.1O₁₇ ceramic sintered at 1575 °C for 4 h.     

Dielectric properties of Be(IO<Subscript>3</Subscript>)<Subscript>2</Subscript>⋅4H<Subscript>2</Subscript>O crystals

The article studies the dielectric properties, dc conductivity and ac conductivity of Be(IO₃)₂⋅4H₂O single crystals. The dielectric constant ε has been defined for the three directions of the vectors a, b and c in the crystals in the temperature interval 280–340 K and frequency range 100 Hz–10⁶ Hz. The crystals show strongly expressed anisotropy, at 20 ^∘C and frequency 100 Hz ε_a = 235, ε_b = 30 and ε_c = 85. The frequency dependence of ε is evidence of the presence of low-frequency relaxation polarization in the crystals. The activation energies of the three directions in the crystals have been derived from the temperature dependence of dc conductivity, and they are 1.03 eV, 0.836 eV and 1.2 eV respectively.     

Studies on a.c. properties of Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> perovskites

A.c. measurements were preformed on bulk samples of Ca_1−x Sr _x TiO₃ (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 10³–10⁵ Hz . The experimental results indicate that the a.c. conductivity σ_a.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function of frequency is well described by a power law Aω ^S with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response (UDR) behavior.