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.     

Microwave properties of the ceramic compositions M2+Ti4+ 1−x Me4+O3

The systems MgZr _x TiO₃, Mg_1?y Ca _y Ti_1?x Sn _x O₃, where Ti⁴⁺ is partially substituted by Zr⁴⁺ or Sn⁴⁺, and a series of compositions Mg (Ca_1.5Ta_0.2) _x Ti_1?x O₃, where Ti⁴⁺ is partially substituted by the four-valent cation (Ca_1.5Ta _0.2)⁴⁺, have been synthesized. For all compositions it was found that the permittivity ε_r and quality factor Q decreased monotonically with increasing substitution factor x. The measurements were carried out within the frequency range 9–11 GHz. At lower x, the quality factor had high values, so that such compositions could be used as microwave resonators with controllable parameters (for instance, for satellite television). The relationships between Q and x which have been obtained, together with the changes in density, are interpreted.     

Influence of Zr doping on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Pure and Zr-substituted CaCu₃(Ti_1−x Zr _x )₄O₁₂ (x = 0, 0.01, 0.02, 0.03) ceramics were prepared by the Pechini method. X-ray powder diffraction analysis indicated the formation of single-phase compound, and all the diffraction peaks were completely indexed by the body-centered cubic perovskite-related structure. The effects of Zr⁴⁺ ion substituting partially Ti⁴⁺ ion on the dielectric properties were investigated in frequency range between 100 Hz and 1 GHz. The low frequency (f ≤ 10⁵ Hz) dielectric constant decreases with Zr substitution and the high frequency (f ≥ 10⁷ Hz) dielectric constant is unchanged. Interestingly, a low-frequency relaxation was observed at room temperature through Zr substitution. The observed dielectric properties in Zr-substituted samples were discussed using the internal barrier layer capacitor model. A corresponding equivalent circuit was adopted to explain the dielectric dispersion. The characteristic frequency of low-frequency relaxation rises due to the decrease of the resistivity of grain boundary with Zr substitution, which is likely responsible for the large low-frequency response at room temperature.     

The effect of Ba2+ doping on the structure of SrBi4Ti4O15

In this paper, bi-layered structural ferroelectric materials Sr_1–x Ba _x Bi₄Ti₄O₁₅(SBBT) (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were prepared using sol–gel method. The stable precursors were fabricated by mixing the salts of strontium (Sr), barium (Ba), bismuth (Bi) and titanium butoxide in acetic acid together with ethanolamine as a catalyzer and acetylacetone as a stable agent. The structural evolution of SBBT after Ba²⁺ doping was studied. The experimental results confirm that complete solid solutions of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ are formed. The perovskite lattice will expand after the doping of Ba²⁺ because of the difference of ionic radii of strontium and barium cations, which will lead to increasing of the lattice spacing. With the increase of the content of Ba cations the grain size of SBBT powder increases, the granularity distribution widens and average particle size of SBBT powder also increases. The average particle size of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ is 82.5 and 165.2 nm, respectively.     

Phase Composition of Zn2TiO4–Zn2ZrO4Materials Prepared by Low-Temperature Plasma Synthesis and Ceramic Processing

Zn₂Ti_{1 – x} Zr _x O₄solid solutions were prepared by low-temperature plasma synthesis and solid-state reactions, and their properties were compared. The Zn₂TiO₄–Zn₂ZrO₄pseudobinary system was found to contain two broad solid-solution ranges with inverted spinel structures: phase at 0 < x< 0.3, witha= 8.474–8.555 Å, and phase at 0.5 < x< 1.0, with a= 8.615–8.740 Å and c= 8.733–9.120 Å. The conductivity of the solid solutions notably decreases upon substitution of Zr⁴⁺for Ti⁴⁺and varies exponentially with temperature.     

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.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

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.     

Microstructure and dielectric relaxor behavior of Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3–BaBi4Ti4O15 ceramics by tape casting

Plate-like BaBi₄Ti₄O₁₅ powders were used to fabricate 0.952[Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃]–0.048BaBi₄Ti₄O₁₅(abbr. BZCT-BBT) ceramics by tape casting. The microstructure and dielectric relaxor behaviors of BZCT-BBT ceramics were investigated. BZCT-BBT ceramics can be sintered well at 1,100?°C and mainly consisted of tetragonal perovskite phase and BaBi₄Ti₄O₁₅ (abbr. BBT) phase. The lattice constants decrease as the sintering temperature increases due to substitution of Bi³⁺ for the A-site atoms of the perovskite structure. There is no obvious difference between the structure in the perpendicular and parallel directions, however, an evident difference of dielectric properties in the two directions is observed. Comparing with Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃(abbr. BZCT) ceramics, BZCT-BBT ceramics show obvious relaxor characteristics which are evidenced by the degree of diffuseness γ calculated using the modified Curie–Weiss law. Meanwhile, the addition of BBT decreases T_m, which results from the decrease of grain size. The reduction of ε_m is mainly caused by phase structure deviation from the coexisting rhombohedral and tetragonal structure to single tetragonal.     

Effect of sintering temperature on the grain growth and electrical properties of barium zirconate titanate ferroelectric ceramics

In the present work, structural, dielectric and ferroelectric properties of barium zirconate titanate ferroelectric ceramics have been investigated. The specimens were synthesized using a solid state reaction technique. The XRD analysis reveals that the synthesized compound was formed with no secondary phases. As the sintering temperature increases from 1,200 to 1,300 °C, the average grain size is observed to increase from ~0.39 to ~6.15 μm. The dielectric measurements as a function of temperature show a decrease in Curie temperature (T_C) on increasing the sintering temperature. The decrease in Curie temperature is attributed to the substitution of Zr⁺⁴ whose ionic radius is larger than Ti⁺⁴. A large increase in the dielectric constant with the increase in grain size is observed. The remanent polarization is also observed to increase with the increase in grain size.     

Microstructure,dielectric, and energy storage performance of (Zn1/3Nb2/3)4+ complex-ion modified (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics

In this study, (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)_1-x(Zn_1/3Nb_2/3)_xO₃ ceramics were synthesized by conventional solid-phase methods, referred to as BCZT-xZN (x?=?0.0, 0.1, 0.2, 0.3, 0.4). The effects of adding different contents of (Zn_1/3Nb_2/3)⁴⁺ ion on the microstructure, dielectric and ferroelectric properties of BCZT ceramics were studied. Scanning electron microscopy (SEM) results showed that the average particle size of the samples was significantly reduced after the addition of (Zn_1/3Nb_2/3)⁴⁺ ion, and a second phase appeared when the addition amount was?≥?0.3. The dielectric properties show that with (Zn_1/3Nb_2/3)⁴⁺ ion replacing the B-site of BCZT ceramics, the dielectric constant decreases significantly and the Curie temperature decreases below room temperature. At the same time, we observed that the ceramic has good stability to temperature (-150 °C–200 °C) and frequency (10²–10⁶ Hz) changes. The addition of (Zn_1/3Nb_2/3)⁴⁺ ion can significantly reduce the residual polarization and improve the breakdown strength of ceramics. When x?=?0.3, The maximum energy storage density of ceramics is 0.994 J/cm³, which is about four times higher than that of pure BCZT ceramic (0.25 J/cm³). These findings fully demonstrate the great potential of BCZT ceramics in energy storage.

     

Effect of Isovalent Ba-Site Substitutions on the Properties of (Ba1 – x – y M y Y x )TiO3(M = Ca, Sr, Pb) PTCR Ceramics

An approach is proposed for fabricating fine-grained, low-resistivity BaTiO₃-based PTCR ceramics via partial isovalent substitutions on the Ba site. The grain size of the ceramics thus prepared is shown to decrease as the ratio of ionic radii r(Ba²⁺)/r(M²⁺) (M = Ca, Sr, Pb) increases. Isovalent substitutions on the Ba site narrow down the range of donor dopant (yttrium) concentrations in which PTCR materials can be prepared. The experimental results agree well with thermodynamic calculations under the assumption that the materials contain the Y³⁺Ti³⁺O₃ phase, as suggested by ESR data, which point to the presence of Y³⁺–Ti³⁺ associates. Partial calcium, strontium, and lead substitutions on the Ba site reduce the average grain size of PTCR ceramics, which is probably due to the lattice strain arising from the isovalent substitution. Partial replacement of Ba²⁺ with mixtures of different isovalent elements (e.g., Sr²⁺ and Pb²⁺) offers the possibility of obtaining fine-grained, low-resistivity PTCR ceramics, without changing the phase transition temperature.     

Effect of doping Ca ions on structural and electrical properties of Ba(Zr0.05Ti0.95)O3 electroceramics

Polycrystalline samples of (Ba_1–zCa_z)(Zr_0.05Ti_0.95)O₃ (z=0, 0.03, 0.06 and 0.09) (BCZT) belonging to perovskite ferroelectric were prepared by a high-temperature solid-state reaction technique. Preliminary room temperature X-ray study confirmed the formation of a single phase compound in orthorhombic crystal structure. Detailed studies of dielectric parameters as a function of temperature at 10 kHz suggests that the substitution of Ca²⁺ ion at the Ba-site and Zr⁴⁺ at Ti-site has a strong effect on the dielectric properties of BaTiO₃.     

Magnetization and initial permeability studies of Nd3+ substituted Zn-Mg ferrite system

Polycrystalline ferrites, Zn _x Mg_1−x Fe_2−y Nd _y O₄ (x=0·00, 0·20, 0·40, 0·60, 0·80 and 1·00;y=0·00, 0·05 and 0·10), were prepared by standard ceramic method. The compositions, on characterization by X-ray diffraction, showed formation of single phase cubic spinels. Magnetic study of the compositions showed increase in magnetic moment,nβ, with Zn²⁺ concentration up tox=0·4 and a decrease thereafter. This was attributed to the existence of canted spin. The compositions forx=0·8 and 1·0 showed paramagnetic behaviour at and above room temperature. The substitution of Nd³⁺ ion caused reduction in the magnetic moment and Curie temperatures. Substituted Nd³⁺ ion showed its occupancy on octahedral (B) site. The dependence of the initial permeability was studied in the temperature range 298 K-700 K. This μ_i-T curve reflects the positive temperature coefficient of initial permeability for the compositionsx≤0·4 andy=0·00. On substitution of Nd³⁺ ion (i.e.y=0·05 and 0·10), the μ_i-T curves flatten, showing almost temperature independence of initial permeability. This is explained by positive contribution to the anisotropy constant,K ₁, by substituted rare-earth, Nd³⁺ ion.     

Effect of Zr+4 ion substitution on the structural, dielectric and electrical properties of Sr5LaTi3Nb7O30 ceramics

Polycrystalline Zr-modified Sr₅LaTi₃Nb₇O₃₀ compound was prepared by a high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of compound in an orthorhombic system at room temperature. Detailed studies of the dielectric parameters (dielectric constant and tangent loss) as a function of frequency (1–100 kHz) at different temperature (150 to 650 K) were carried out. It was found that as Zr⁺⁴ concentration increases in Sr₅LaTi_{3 – x} ZrxNb₇O₃₀, the value of dielectric constant decreases. These compounds show ferroelectric-paraelectric phase transition of diffuse type at 283, 305 and 320 K for x = 0, 1 and 2 respectively. The transition temperature (T _c) shifts towards higher temperature and maximum dielectric constant value (_max) decreases with increasing Zr⁺⁴ concentration for x = 0 to x = 2. When Ti⁺⁴ cations were completely replaced by Zr⁺⁴ cations (i.e., Sr₅LaZr₃Nb₇O₃₀), the compound does not show any phase transition. Impedance-spectroscopic studies provided an insight into the electrical properties and understanding of relaxation behavior of the material. Measurement of electrical conductivity as a function of temperature suggests that the compounds have a negative temperature coefficient of resistivity (NTCR) with a typical semiconductor behavior.     

Effects of La3+ doping ions on dielectric properties and formation of Schottky barriers at internal interfaces in a Ca2Cu2Ti4O12 composite system

Influences of La³⁺ substitution on the dielectric properties and formation of Schottky barriers at internal interfaces of a Ca₂Cu₂Ti₄O₁₂ (CaTiO₃/CaCu₃Ti₄O₁₂) composite system were investigated. It was found that electrostatic potential barrier height was greatly reduced by doping with La³⁺, leading to a large decrease in the total resistance of internal interfaces between grains. This observation was attributed to the creation of conduction electrons, which were possibly induced by electrical charge compensation of La³⁺ substitution into Ca²⁺ sites. Variations in the dielectric properties of La³⁺-doped CaTiO₃/CaCu₃Ti₄O₁₂ composite ceramics and nonlinear properties can be described based on the electrical responses at the internal interfaces between CaCu₃Ti₄O₁₂–CaCu₃Ti₄O₁₂ grains and CaTiO₃–CaCu₃Ti₄O₁₂ grains. Influence of possible charge compensation due to different levels of La³⁺ dopant on the formation of potential barriers was discussed.     

Effect of piezoelectric grain size on magnetoelectric coefficient of Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 particulate composites

This study investigates the variation of magnetoelectric (ME) coefficient as a function of the piezoelectric grain size in the composite system of 0.8 Pb(Zr_0.52Ti_0.48)O₃–0.2 Ni_0.8Zn_0.2Fe₂O₄. It was found that as the piezoelectric-phase grain size increases the overall resistivity, piezoelectric, dielectric, and ferroelectric property of the composite increases and saturates above 600 nm. Below 200 nm average grain size, piezoelectric and dielectric properties decrease rapidly. The ferroelectric Curie temperature was found to decrease from 377 to 356 °C as the average grain size decreases from 830 to 111 nm. ME coefficient of the composite showed a rapid change below grain size of 200 nm and was found to saturate above 600 nm to a value of 155 mV/cm.Oe.     

Effect of substitution of titanium by magnesium and niobium on structure and piezoelectric properties in (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> ceramics

To develop new (Bi_1/2Na_1/2)TiO₃-based ceramics with excellent piezoelectric properties, the similarities and the differences between PZT and (Bi_1/2Na_1/2)TiO₃ ceramics were analysed. Based on the analysis, a new (Bi_1/2Na_1/2)TiO₃-based piezoelectric ceramic of B-site substitution of complex ions (Mg_1/3Nb_2/3)⁴⁺ for Ti⁴⁺ was prepared by a conventional ceramic technique, and effect of complex ions (Mg_1/3Nb_2/3)⁴⁺ addition on the microstructure, dielectric and piezoelectric properties was investigated. The results show that all compositions are mono-perovskite phase and the grain size increases with increasing content of (Mg_1/3Nb_2/3)⁴⁺. The piezoelectric constant, d ₃₃, first increases and then decreases, and electromechanical coupling factor, k _p, varies insignificantly with increasing content of (Mg_1/3Nb_2/3)⁴⁺.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Crystal structure,energy gap and photoluminescence investigation of Mn2+/Cr3+-doped ZnS nanostructures by precipitation method

Mn added ZnS (Zn_0.97Mn_0.03S) and Mn–Cr-doped ZnS (Zn_0.95Mn_0.03Cr_0.02S) nanostructures were synthesized by co-precipitation process. XRD pattern confirmed the cubic phase with highest intensity along (111) orientation. The shrinkage of crystallite size from 36 Å (Zn_0.97Mn_0.03S) to 26 Å (Zn_0.95Mn_0.03Cr_0.02S) and the influence of Cr/Mn on microstructural, optical and photoluminescence properties in ZnS were investigated. The substitution of Cr in Zn_0.97Mn_0.03S lattice not only diminished the crystallite size and also produced more defect-associated luminescent activation centres. The elevated micro-strain from 9.71?×?10^–3 (Zn_0.97Mn_0.03S) to 13.11?×?10^–3 (Zn_0.95Mn_0.03Cr_0.02S) by Cr substitution is due to the decrease of size and the higher micro-strain at Cr?=?2% is owing to the drop off of activation energy which is originated from higher electro-negativity of Cr ions than Zn²⁺ ions. The enhanced lattice parameters by Cr doping may be due to the coexistence of both Cr³⁺ ions and Cr²⁺ ions where the existence of Cr²⁺ ions is higher than Cr³⁺ ions and substitute Zn²⁺ basic ions with the ionic radius of 0.74 Å in the Zn–Mn–S host lattice. The presence of Zn²⁺, Mn²⁺ and Cr³⁺ ions in Zn–Mn–Cr–S lattice was confirmed by XPS spectra. SEM/TEM micrographs explored the microstructure and confirmed the sized reduction by Cr doping. The elevation in band gap from 3.50 eV (Zn_0.97Mn_0.03S) to 3.63 eV (Zn_0.95Mn_0.03Cr_0.02S, ?E_g?~?0.13 eV) by Cr addition was explained by Burstein–Moss effect and reduced crystallite size. The tuning of band gap and crystallite size of basic ZnS nanostructure by Mn/Cr substitution encourages these materials for modern electronic applications. FTIR spectra established the occurrence of Mn/Cr in Zn–S lattice by their characteristic bondings. The elevated yellowish-orange emission at 594 nm in Mn/Cr substituted ZnS is due to the exchange communication among the s–p electron states of Cr³⁺, Mn²⁺ and Zn²⁺ ions in Zn–S lattice. The inclusion of Mn /Cr provides an efficient control over modification of various emissions which suggests their applications in organic LED materials.