Nanocrystalline PbIn<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> ceramics and its properties

A ferroelectric relaxor PbIn_0.5Nb_0.5O₃ (PIN) ceramics has been obtained using a modified ceramic technology, with the sintering stage preceded by compression and shear straining of the synthesized charge in Bridgman anvils. The dimensions of ceramic grains after this pretreatment are spread over a range from 100 to 1250 nm. A comparative investigation of the properties of PIN ceramics obtained using the standard and modified technology showed that the proposed mechanical action at the charge preparation stage can be used for controlled modification of the properties of ferroelectric ceramics.     

Physical properties of lead-free BaFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics obtained from mechanochemically synthesized powders

Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe_1/2Nb_1/2O₃ (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe_1/2Nb_1/2O₃ ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics.     

Structure and dielectric characteristics of PbFe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> single crystals grown under different conditions

The structure and dielectric and magnetic characteristics of plumbum ferroniobate crystals grown from a solution–melt containing potassium fluoride have been investigated. The obtained crystals have a cubic shape, 4-mm edges, and a rhombohedral structure at room temperature. Iron ions in the samples have the valence state of Fe³⁺. A change in the Mössbauer spectra with a change in temperature has been registered; this is indicative of strong diffusion of the magnetic phase transition in the range from–130 to–230°C, which is enhanced due to incorporation of fluorine atoms into the structure of the basic compound accompanying the synthesis process and clusterization of this structure. The latter phenomena also lead to a decrease in the temperature of transition from the ferro- to paraelectric phase.     

Microwave dielectric properties of Ba<Subscript>5</Subscript>Nb<Subscript>4</Subscript>O<Subscript>15</Subscript> ceramic by molten salt method

Ba₅Nb₄O₁₅ powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in a certain proportion. Subsequent calcination of the mixtures led to Ba₅Nb₄O₁₅ powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba₅Nb₄O₁₅ powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba₅Nb₄O₁₅ ceramics with good microwave dielectric properties of ε_r = 39.2, Q × f approximated as 27,200 GHz and τ _f  = 72 ppm/°C have been obtained.     

Structural,optical spectroscopy,optical conductivity and dielectric properties of BaTi<Subscript>0.5</Subscript>(Fe<Subscript>0.33</Subscript>W<Subscript>0.17</Subscript>)O<Subscript>3</Subscript> perovskite ceramic

Fe and W co-substituted BaTiO₃ perovskite ceramics, compositional formula BaTi_0.5(Fe_0.33W_0.17)O₃, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electron microscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi_0.5(Fe_0.33W_0.17)O ₃ sample was performed in the cubic double and hexagonal setting of the \(\text {Fm}\boldsymbol {\bar {{3}}\mathrm {m}}\) and P6 ₃ /mmc space groups. Spectral dependence of optical parameters; real and imaginary parts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data using Wemple–DiDomenico single-effective-oscillator model.     

Structural and dielectric properties of PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions synthesized at high pressures and temperatures

(1 ? x)PbMg_1/3Nb_2/3O₃ · xPbZrO₃ (1 ? x)PMN · xPZ) solid solutions have been synthesized at a pressure of 5 GPa and temperatures from 1300 to 1700 K, and their structural and dielectric properties have been studied. The composition dependences of the average unit-cell parameter and dielectric permittivity for the solid solutions indicate that the PMN-PZ system has a morphotropic phase boundary near x = 0.65. The solid solutions have a cubic structure for x < 0.65, a rhombohedral structure in the range 0.65 < x < 0.9, and an orthorhombic structure (similar to that of PbZrO₃) for x > 0.9. The temperature and frequency dependences of dielectric permittivity suggest that the (1 ? x)PMN · xPZ samples with x < 0.65 consist of two ferroelectric phases: a relaxor with antipolar dipole order and a normal ferroelectric with a diffuse phase transition. The effect of annealing temperature on the ferroelectric state of the samples with x < 0.65 is examined. In the composition range 0.65 < x < 0.9, the samples have normal ferroelectric properties, independent of annealing temperature.     

Structural,dielectric and electrical properties of CaBa<Subscript>4</Subscript>SmTi<Subscript>3</Subscript>Nb<Subscript>7</Subscript>O<Subscript>30</Subscript> ferroelectric ceramic

The polycrystalline sample of CaBa₄SmTi₃Nb₇O₃₀, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction analysis shows the formation of single-phase compound with an orthorhombic structure at room temperature. Scanning electron micrograph of the material shows uniform distribution of grains. 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 198°C, and exhibits non-relaxor kind of diffuse phase transition. The ferroelectric nature of the compound has been confirmed by recording polarization-electric field hysteresis loop. Piezoelectric and pyroelectric studies of the compound have been discussed in this paper. Electrical properties of the material have been analyzed using complex impedance technique. The Nyquist plots manifest the contribution of grain boundaries (at higher temperature), in addition to granular contribution (at all temperatures) to the overall impedance. The temperature dependence of dc conductivity suggests that the compound has negative temperature coefficient of resistance (NTCR) behaviour. The frequency dependence of ac conductivity is found to obey Jonscher’s universal power law. The observed properties have been compared with calcium free Ba₅SmTi₃Nb₇O₃₀ compound.     

Textured BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramic synthesized by laser rapid solidification method and its dielectric properties

Textured poly crystalline barium dititanate BaTi₂O₅ (BT2) ceramics with a preferred 〈010〉 orientation were synthesized by laser rapid solidification method, with a CO₂ laser. The 〈010〉 orientation of the BT2 is along the laser incident direction, and the orientation factor (f) and relative density of the unannealed BT2 sample are 0.40 and 96.2%, respectively. The two quantities increase with increasing annealing time, and reach the maximum values of 0.42 (annealed at 1,000 °C for 12 h) and 97.5% (annealed at 1,000 °C for 24 h), respectively. The images of scanning electron microscopy reveal that the BT2 are composed of flake-like microstructures with the maximum thickness of 20 μm and dimension of 0.6 mm, which are parallel to the laser incident direction. The measured Curie temperature (T _c) and the maximum dielectric constant (ε_max) are 443 and 6,000 °C, respectively.     

The effect of a constant electric field on the structural parameters of ferroelectric PbSc<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> crystals

The effect of a constant electric field on the polarization and structural parameters of ferroelectric lead scandium niobate (PbSc_0.5Nb_0.5O₃) crystals was studied using X-ray diffraction. Application of a constant electric field leads to splitting of the Bragg diffraction peaks. It is shown that this behavior is most probably explained by the formation of a new phase.     

Fabrication and dielectric properties of textured Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ceramics by RTGG method

Grain-oriented Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBTBT) ceramics were fabricated by reactive-templated grain growth using plate-like Bi_2.5Na_3.5Nb₅O₁₈ (BNN) as templates. The specimens are composed of NBTBT perovskite phase and BNN lay-structured phase. Textured ceramics have a brick-wall microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit an {h00} preferred orientation. The texture fraction increases initially, and then decreases with increasing sintering temperature. The optimal sintering temperature is 1,185 °C where the texture fraction has a maximum value of 0.58 and d₃₃ is 98 pC/N. The textured NBTBT ceramics show evidence of relaxor ferroelectrics with diffuse phase transition and frequency dispersion because of composite biphasic structure.     

Dielectric and piezoelectric properties of MnO<Subscript>2</Subscript>-doped K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.92</Subscript>Sb<Subscript>0.08</Subscript>O<Subscript>3</Subscript> lead-free ceramics

Lead-free MnO₂-doped K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have been studied. Our results show that a small amount of MnO₂ (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics. The co-effects of MnO₂ doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping possesses optimum propeties: d ₃₃ = 187 pC/N, k _P = 47.2%, ε _r = 980, tanδ = 2.71% and T _c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T _O-T ~ 150 °C), the K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping exhibits a good thermal stability of piezoelectric properties.     

Template synthesis of BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> ordered nanowire arrays by a new method

A method that the precursor is generated in situ and shaped into the one dimension nanostructure in the nanochannels of the anodic alumina membrane (AAM) template is described. The high-aspect ratio nanowire array of the BaFe₁₂O₁₉ was prepared by means of this method. Electron microscope images showed that the BaFe₁₂O₁₉ nanowire array was abundant, uniformly distributed and well-ordered in the large area. It is estimated from the electron microscope images that the diameter of the individual nanowire is about 60 nm and the length was corresponding to the thickness of the applied AAM template. The analysis of X-ray diffraction demonstrated that the BaFe₁₂O₁₉ nanowires have a hexagonal structure of the pure phase BaFe₁₂O₁₉.     

Low-temperature sintering and microwave dielectric properties of Mg<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript>-LMZBS composites

The Mg₃B₂O₆ ceramics with lithium magnesium zinc borosilicate (LMZBS) glass were prepared at a lower sintering temperature. The effects of the glass addition on the densification, phase development, microstructure and microwave dielectric properties of the Mg₃B₂O₆ ceramics were investigated. The addition of LMZBS glass improved the densification and lowered the sintering temperature of Mg₃B₂O₆ ceramics from 1,300 to 950 °C. X-ray diffraction patterns showed that Mg₃B₂O₆ transformed into Mg₂B₂O₅ and a new phase, Li₂ZnSiO₄, crystallized from the glass phase. Because of the high dielectric performance of these phases, Mg₃B₂O₆ mixed with 55 wt% LMZBS sintered at 950 °C for 3 h had ε_r = 6.8, Q × f = 50,000 GHz, and τ_f = ?64 ppm/°C at 7.28 GHz. The chemical compatibility of ceramic-glass composites with Ag was also investigated for LTCC.     

Low temperature sintering and microwave dielectric properties of Zn<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramic

Crystal structure and dielectric properties of Zn₃Mo₂O₉ ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn₃Mo₂O₉ crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity (ε _r ) of 8.7, a quality factor (Q?×?f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency (τ _f ) of around ??79 ppm/°C. With 5 wt% B₂O₃ addition, the sintering temperature of Zn₃Mo₂O₉ ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε _r ?=?11.8, Q?×?f?=?20,000 GHz, and τ _f = ??79.5 ppm/°C were achieved.     

Investigation of density of states and electrical properties of Ba<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Bi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> nanoceramics prepared by chemical route

Barium-cobalt-bismuth-niobate, Ba_0.5Co_0.5Bi₂Nb₂O₉ (BCoBN) nanocrystalline ferroelectric ceramic was prepared through chemical route. XRD analysis showed single phase layered perovskite structure of BCoBN when calcined at 650 °C, 2 h. The average crystallite size was found to be 18 nm. The microstructure was studied through scanning electron microscopy. The dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C. The dielectric constant and dielectric loss plot with respect to temperature both indicated strong relaxor behavior. Frequency versus complex impedance plot also supported the relaxor properties of the material. The impedance spectroscopy study showed only grain conductivity. Variation of ac conductivity study exhibited Arrhenius type of electrical conductivity where the hopping frequency shifted towards higher frequency region with increasing temperature. The ac conductivity values were used to evaluate the density of state at the Fermi level. The minimum hopping distance was found to be decreased with increasing temperature.     

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.     

Effects of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> additive on sintering behavior and microwave dielectric properties of ZnTa<Subscript>2</Subscript>O<Subscript>6</Subscript> ceramics

ZnTa₂O₆ ceramics with various amount of Al₂O₃ additive were synthesized by a conventional mixed-oxide route. The grain growth of ZnTa₂O₆ ceramics was accelerated with Al₂O₃ additive. However, excessive addition (>1.0 wt%) of Al₂O₃ leaded to abnormal grain growth. With Al₂O₃ addition, the Al₂O₃ additive did not solubilized into ZnTa₂O₆ structure but resulted in forming the second phase. The Al₂O₃ addition resulted in the lower sintering temperature of ZnTa₂O₆ ceramics and improved microwave dielectric properties. The dielectric constant (ε_r) of the samples did not change much and ranged from 32.41 to 34.33 with different amount of Al₂O₃ addition. The optimized quality factor (Q × f) was higher than 70,000 GHz as a result of the denser ceramics. The temperature coefficient of resonant frequency (τ _f ) of the doped ZnTa₂O₆ ceramics could be optimized to near-zero.     

Structural studies of a new electroceramic composite: Pb(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> (PFN)-Cr<Subscript>0.75</Subscript>Fe<Subscript>1.25</Subscript>O<Subscript>3</Subscript>(CRFO)

A study of the structural characteristics of the composites [Pb(Fe_0.5Nb_0.5)O₃(PFN)] _x -[Cr_0.75Fe_1.25O₃(CRFO)]_100?x (x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and ⁵⁷Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe⁺³. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination.     

Effect of nonstoichiometry on the structure and microwave dielectric properties of Ba(Co<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>

Polycrystalline nonstoichiometric Ba(Co_1/3Nb_2/3)O₃ (BCN) materials have been synthesized and investigated. Deviations from stoichiometry have been shown to lead to the formation of crystalline Ba₆CoNb₉O₃₀ (barium deficiency) and Ba₈CoNb₆O₂₄ (cobalt deficiency). The effect of phase composition on the microwave dielectric properties of BCN has been studied. The results demonstrate that the dielectric properties of BCN-based materials can be tuned by varying cobalt content. The materials obtained are high-Q microwave dielectrics with temperature-stable properties.