Application feasibility of Pb(Zr,Ti)O3 ceramics fabricated from sol–gel derived powders using titanium and zirconium alkoxides

It is believed that what may be termed the ‘Nanoscaled Century’ will lead to a new industrial revolution, particularly in terms of sol–gel methods of assembly for nanostructure devices. A propyl alcohol (1-Pro) based sol–gel chemical has been developed to replace 2-methoxyethanol (MOE), 1,1,1-tris(hydroxymethyl)ethane (THOME) for the fabrication of PbZr_0.53Ti_0.47O₃ (PZT) piezoelectric ceramics. This chemical is prepared from sol–gel derived powders that are near to the morphotropic phase boundary (MPB). The pyrochlore phase was still apparent when calcining at 900 °C with a shorter calcining time, such as 30 min. However, it disappeared for longer calcining times, for example 3 h or more. From the results of the analysis, PZT ceramics calcinations at 900 °C for 4 h, and sintering at 1100 °C for 2 h could reach a pyrochlore-free crystal phase with relative density of approximately 7.9 g/cm³—close to 98% of the theoretical value. The P–E hysteresis loop, measured by the Sawyer–Tower circuit, revealed that the remanent polarization (P_r) and coercive field (E_c) were 8.54 μC/cm² and 15.6 kV/cm, respectively. The vibration modes of the PZT ceramics were between 150 and 1.5 MHz. Morevoer, under such processing conditions the PZT piezoceramics had uniform grain size distribution less than 1 μm and zero temperature coefficient of resonant frequency (TCF). In summary, the PZT ceramics derived from the sol–gel method were confirmed to possess excellent piezoelectric properties. Furthermore, the processing temperatures were scaled down by 100–200 °C, compared to conventional oxide reaction. Finally, from an energy-saving viewpoint, this experiment can potentially make a very positive contribution.     

The origin of defects formation in nanosized zirconia

In the present work, we provide evidence of an increase in the Zr³⁺ paramagnetic center concentration under colloidal transformation in ZrO₂ prepared by the totally inorganic sol–gel method. The samples of thermally treated (100–950 °C in air) ZrO₂ precipitates and dried sol–gel products—xerogels—were examined by TEM, XRD, DTA, EPR and IR-spectroscopy. Under the same heat treatment condition, the concentration of Zr³⁺ (axially symmetric signal at g_⊥ = 1.977–1.979 and g₆ = 1.958–1.963) became higher in the xerogel samples rather than in precipitate samples and reached the maximum (∼ 10¹⁸ g^− 1 in xerogel) after calcinations at 500 °C in air.     

Synthesis of RuSr2GdCu2O8 − δ superconductors by the sol–gel route

The RuSr₂GdCu₂O_8 − δ (Ru-1212) superconductors have been prepared through the sol–gel route. We found that 1030 °C is the optimum annealing temperature for the formation of the Ru-1212 superconductors synthesized by the sol–gel route. X-ray powder diffraction analysis indicates that nearly all the peaks from the samples can be indexed to a single phase of Ru-1212, tetragonal symmetry with lattice parameters a = b = 3.382 Å, c = 11.478 Å and space group I4/mmm. The RuSr₂GdCu₂O_8 − δ superconductors prepared by the sol–gel method exhibit onset transition temperature T_c-onset near 55 K and zero resistance temperature T_c-zero at 45 K.     

Electrical properties of lead zirconate titanate thick films prepared by hybrid sol–gel method with multiple infiltration steps

High-quality ferroelectric thick films are required for various piezoelectric applications including high-frequency transducers and microelectromechanical systems. In this work, we report the fabrication of dense crack-free lead zirconate titanate (PZT) thick films on Pt-coated Si substrates using commercial PZT powder dispersed in a sol–gel precursor solution without viscous additives. Preannealed films were infiltrated with the same solution and heat treated at 500 °C. Dielectric and ferroelectric properties of the films are found to be strongly dependent on the number of infiltration steps reaching sufficiently high values: dielectric constant ∼2270 and remanent polarization ∼35 μC cm⁻². Moderate coercive field of 60 kV cm⁻¹ and low dielectric loss ∼0.04 are observed in these films. Effective longitudinal piezoelectric coefficient d₃₃ also depends on the number of infiltrations demonstrating remanent value of ∼80 pm V⁻¹ for eight infiltration steps. The results show the suitability of hybrid sol–gel method for the fabrication of PZT thick films for dielectric and piezoelectric applications.     

On the synthesis and dielectric studies of (1 − x)Bi(Mg1 / 2Zr1 / 2)O3 − xPbTiO3 piezoelectric ceramic system

Scandium free piezoelectric ceramics of the composition (1 − x)Bi(Mg_1 / 2Zr_1 / 2)O₃ − xPbTiO₃ (BMZ − xPT) were fabricated by the solid state reaction method. Dielectric and structural properties were measured and phase diagram was constructed from the temperature dependent dielectric and impedance data. The morphotropic phase boundary (MPB) was found to be located in the range 0.55 < x < 0.60 with paraelectric–ferroelectric phase transition temperature, T_C (∼ 280 °C). The ceramics near the MPB showed high room temperature dielectric constant (∼ 1387). The room temperature values of the remanent polarization (P_r) and coercive filed (E_C), were ∼ 29 μC/cm² and ∼ 23 kV/cm, respectively.     

Processing and electrical properties of (1 − x)[(1 − y)(Pb(Mg1/3Nb2/3)O3)–y(Pb(Yb1/2Nb1/2)O3)]–xPbTiO3 ceramics

Ferroelectric ceramics in the vicinity of morphotropic phase boundary (MPB) with compositions represented as (1 ? x)[(1 ? y)(Pb(Mg_1/3Nb_2/3)O₃)–y(Pb(Yb_1/2Nb_1/2)O₃)]–xPbTiO₃ were prepared by solid state reaction. The addition of PYbN to PMN–PT decreased the sintering temperature from 1200 °C (y = 0.25) to 1000 °C (y = 0.75). The PT content, where the MPB was observed, increased with the PYbN addition. A remanent polarization value of 28.5 µC/cm² and a coercive field value of 11 kV/cm were measured from 0.62[0.25PMN–0.75PYbN]–0.38PT ceramics, which were close to the ones measured from PMN–0.32PT ceramics. In addition, the Curie temperature was found to increase with PYbN additions.     

Low-temperature sintering and microwave dielectric properties of CaTi1−x(Fe0.5Nb0.5)xO3 ceramics with B2O3 addition

CaTi_1−x(Fe_0.5Nb_0.5)_xO₃ (0 ≤ x ≤ 1) dielectrics were synthesized via the solid state reaction route and structure analysis was performed together with the dielectric characterization. The substitution of Ti⁴⁺ by Fe³⁺/Nb⁵⁺ and developed phase were studied by X-ray diffraction. The dielectric constant and temperature coefficient of resonant frequency decrease rapidly with an increase of x. The influence of 1–5 wt.% B₂O₃ as a sintering additive investigated at CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ solid solutions. The dielectric properties were found to strongly depend on the sintering conditions and contents of B₂O₃ additions. ɛ_r = 52.3, Q × f_o = 2930 GHz and T_f = 13 ppm/°C were obtained for CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ specimen 3 wt.% B₂O₃ sintered at 900 °C for 2 h.     

Dopant influence on BST ferroelectric solid solutions family

Solid solutions of the Ba_1−xSr_xTiO₃ (BST) type are very attractive for applications in information technology, but also in microwaves for such electrically controlled devices as phase shifters, tunable filters, steerable antennas, varactors, etc. A family of solid solutions with x = 25, 50, 75, 90% was prepared by standard powder technology-solid state reaction and sintered at 1230 °C and 1260 °C. Dielectric permittivity and loss at low (1 kHz) and high frequency (1 ÷ 2 GHz) were measured on a large temperature range − 200 °C ÷ + 200 °C. The influence of Sr content and of 1 wt.% MgO and 1 wt.% MnO₂ doping on the complex dielectric constant was studied. The dielectric permittivity at high frequencies and room temperature considerably decreases with the increase of Sr content. Similarly, low frequency measurements showed a severe and almost linear decrease of the Curie Point with the increase of Sr fraction. At low Sr content, the measured ceramic densities slowly decrease with Sr fraction and represent about 92% of the X-ray density ρ(g/cm³) ≈ 5.99–0.99·x. At x = 90% Sr concentration, very low-density ceramics were obtained with both sintering temperatures.     

Microwave dielectric properties of BaO–TeO2 binary compounds

A series of BaO–TeO₂ binary ceramic compounds were explored for microwave dielectric applications with ultra-low processing temperatures. During the calcination of mixed BaCO₃ and TeO₂ raw powders, BaTe₄O₉, BaTe₂O₆, BaTeO₃, and Ba₂TeO₅ phases were obtained through the sequential phase formations from Te-rich to Ba-rich phases at temperatures ranging from 500 to 850 °C. Sintering temperatures were as low as only 550 °C for the Te-rich phases. Barium tellurate ceramics exhibited excellent microwave dielectric properties with intermediate dielectric permittivities and high quality factors (Q). The dielectric properties at microwave frequencies were ε_r = 10–21, Q × f = 34,000–55,000 GHz, and TCf = − 51 to − 124 ppm/°C, depending on compositions.     

High dielectric constant and low-loss dielectric ceramics of Ba5LnZnNb9O30 (Ln = La,Nd and Sm)

Polycrystalline Ba₅LnZnNb₉O₃₀ (Ln = La, Nd and Sm) ceramics were prepared as single-phase materials through conventional solid-state ceramics route. The structure was characterized by X-ray diffraction methods and scanning electron microscopy (SEM) and the dielectric properties were measured from − 120 °C to 150 °C. All three compounds are paraelectric phases adopting the filled tetragonal tungsten–bronze (TB) structure at room temperature, and the Curie temperature (at 1 MHz) were − 60, − 25 and − 5 °C for Ba₅LaZnNb₉O₃₀, Ba₅NdZnNb₉O₃₀, and Ba₅SmZnNb₉O₃₀ respectively. At 1 MHz their dielectric constant (ε_r) varies from 258 to 310, dielectric loss (tanδ) from 0.0033 to 0.0068, and the temperature coefficients of the dielectric constant (τ_ε) from − 1220 to − 1390 ppm °C^− 1.     

Preparation,characterization and dielectric properties of Ba5LnZnTa9O30 (Ln=La,Sm) ceramics

Ba₅LnZnTa₉O₃₀ (Ln=La, Sm) ceramics were prepared by high temperature solid-state reaction route. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) methods. They belong to paraelectric phase of filled tetragonal TB structure at room temperature with unit cell a=12.5909(4) Å, c=3.9622(2) Å for Ba₅LaZnTa₉O₃₀; and a=12.5777(4) Å, c=3.9544(2) Å for Ba₅SmZnTa₉O₃₀. At 1 MHz, Ba₅LaZnTa₉O₃₀ has high dielectric constants of 89 with low dielectric loss 0.0067, and temperature coefficients of the dielectric constant (τ_ε) −811 ppm °C⁻¹; Ba₅LaZnTa₉O₃₀ has dielectric constants of 74 with low dielectric loss 0.0035, and τ_ε −474 ppm °C⁻¹.     

Improvement of cycle stability at elevated temperature and high rate for LiNi0.5−xCuxMn1.5O4 cathode material after Cu substitution

A series of Cu-substituted LiNi_0.5−xCu_xMn_1.5O₄ (x = 0, 0.03, 0.05 and 0.08) spinels have been synthesized using a sol–gel method. The results demonstrate that when x = 0.05, the sample (LiNi_0.45Cu_0.05Mn_1.5O₄) exhibits the best electrochemical performance, achieving 124.5 mAh g⁻¹ and 115.0 mAh g⁻¹ at the discharge rates of 5 C and 20 C with the capacity retention of 97.7% and 95.7% after 150 cycles, respectively. Besides, the excellent cycle stability at 55 °C has been demonstrated to retain 96.8% of the maximum attainable discharge capacity (127.3 mAh g⁻¹) at the discharge rate of 5 C after 100 cycles. These data indicate that the LiNi_0.45Cu_0.05Mn_1.5O₄ cathode material has the real potential to be used for high power and high energy lithium ion battery in electric vehicle applications.     

La and Co substituted M-type barium ferrites processed by sol–gel combustion synthesis

The flake-like Ba_1−xLa_xCo_xFe_12−xO₁₉ (x = 0.0–0.4) were synthesized using sol–gel combustion synthesis process followed by the thermal insulation process and heating treatment. The synthesis process was investigated and the structure details, morphology, and magnetic properties were evaluated. TG/DTA was used to investigate the formation mechanism and to identify the thermal insulation temperature at 400 °C followed by the heat treatment temperature at 1200 °C. XRD patterns demonstrated that the unit cell volume and particle size decreased with the increase of the substitution content. The typical particles size was in the range of 1–2 μm in the planar dimension whilst the thickness was in the range of 200–500 nm. It was found from the VSM graphs that the saturation magnetizations M_s reached a maximum of 68.15 emu g⁻¹ at x = 0.3 and then decreases to 64.72 emu g⁻¹ at x = 0.3 whilst the coercivity H_c sustained decreases from 2190.70 to 1181.07 Oe g⁻¹ with substitution content increased from 0 to 0.4.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Microwave dielectric properties of xNd(Zn1/2Ti1/2)O3–(1 − x)CaTiO3 ceramics

The microwave dielectric properties of xNd(Zn_1/2Ti_1/2)O₃–(1 − x)CaTiO₃ have been investigated. The system has been prepared by a conventional solid state ceramic route. Nd(Zn_1/2Ti_1/2)O₃ (NZT) possesses a dielectric constant (ε_r) of 32, a high quality factor (Q × f) of 170,000 GHz and a temperature coefficient of resonant frequency (τ_f) of − 42 ppm/°C. In order to produce a temperature-stable material, the addition of CaTiO₃ leads to a near-zero temperature variation of resonant frequency. In general, the microwave quality factor (Q × f) decreased as x increased and the temperature coefficient of resonant frequency (τ_f) was approximately linearly proportional to permittivity. The dielectric constant decreases from 77 to 32 as x varies from 0.2 to 1.0. The dielectric constant (ε_r) of 45, Q × f value of 56,000 (at 6 GHz) and temperature coefficient of resonant frequency (τ_f) of 0 ppm/°C were obtained for 0.5Nd(Zn_1/2Ti_1/2)O₃–0.5CaTiO₃ ceramics sintered at 1300 °C for 4 h. As the content of x increases, the highest Q × f value of 136,200 GHz for x = 0.8 is achieved at the sintering temperature 1300 °C.     

Powder synthesis and properties of LiTaO3 ceramics

The LiTaO₃ powders with sub micrometer grade grain size have been synthesized successfully using a molten salt method. Lithium tantalate began to form at 400 °C reaction temperature and transformed to pure phase without residual reactants when it was processed at 500 °C for 4 h in static air. The undoped LiTaO₃ ceramics with a Curie temperature about 663 °C were obtained by pressureless sintering at 1300 °C for 3 h. The relative dielectric constant (ɛ_r) increases from 50 to 375 at temperature ranging from 30 to 663 °C and then decreases quickly as the temperature increases above 663 °C. The ceramics shows a relative dielectric constant of 49.4, a dielectric loss factor (tan δ) of 0.007, a coercive field (Ec) of 28.66 kV/cm and a remnant polarization (Pr) of 32.48 μC/cm² at room temperature.     

Raman spectroscopy and dielectric properties of nanoceramic NdFeO3

The nanoceramic NdFeO₃ is synthesized by the sol–gel citrate method. The Rietveld refinement of X-ray diffraction pattern at room temperature (30 °C) shows the orthorhombic Pnma phase with lattice parameters a = 5.576 Å, b = 7.756 Å, c = 5.447 Å. Nano-sized crystallites of NdFeO₃ ranging from 45 to 75 nm have been verified by the transmission electron microscope image. The room temperature Raman spectrum is fitted with the sum of 18 Lorentzian peaks. Eigen frequencies of vibrational modes are calculated using density functional theory under generalized gradient approximation and compared with experimental results. Dielectric spectroscopy study of NdFeO₃ has been performed in the frequency range from 50 Hz to 1 MHz and in the temperature range from 50 °C to 240 °C. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using Cole–Cole equation. The frequency dependent conductivity spectra follow the power law.     

Perovskite phase stabilization and dielectric properties of Pb(Zn1/3Ta2/3)O3–BaTiO3 ceramics

The phase structure and dielectric properties of (1 − x)Pb(Zn_1/3Ta_2/3)O₃–xBaTiO₃ (x = 0.00–0.40) ceramics were investigated. Pure perovskite is obtained when x ≥ 0.24. With increasing BT content, the diffuse phase transition and frequency dissipation of the dielectric constant increase and the dielectric maxima temperature decreases. It is related to the existing of Ba(Zn_1/3Ta_2/3)O₃ paraelectric microregions and the incomplete solid solution reaction between Pb(Zn_1/3Ta_2/3)O₃ and BaTiO₃.     

Microwave dielectric ceramics in (Ca1− xBax)(Zn1 / 3Nb2 / 3)O3 system

(Ca_1−xBa_x)(Zn_1 / 3Nb_2 / 3)O₃ (x = 0–1.0) microwave dielectric ceramics were prepared and investigated. The Ba(Zn_1 / 3Nb_2 / 3)O₃-based solid solution was observed for x = 0.9, and the compositions with x = 0.1–0.7 resulted in the mixture of two phases. Dielectric constant ε_r and temperature coefficient of resonant frequency τ_f of the present ceramics varied anomalously and reached their maximum at x = 0.7–0.9, and these phenomena were originated from the partial substitution of small Ca²⁺ ions for larger Ba²⁺ at A-site. On the other hand, a good combination of microwave dielectric properties (ε_r = 36, Qf = 16,170 GHz, τ_f = − 12 ppm/°C) were obtained at x = 0.1, while the decreased Qf value was observed in other compositions.