Photoluminescence and dielectric properties of LnTiTaO<Subscript>6</Subscript> (Ln = Ce,Pr, Sm) polycrystals

Polycrystalline LnTiTaO₆ (Ln = Ce, Pr, Sm) compounds were prepared in the solid state ceramic route. The powders were calcined between 1250 °C and 1300 °C and sintered between 1480 °C and 1520 °C. The materials were characterized by XRD and SEM. The dielectric properties were measured in the frequency range 1 kHz–5 MHz. The absorption spectra and photoluminescence spectra of the samples were analysed. The materials are useful as gain media in micro lasers because of the optical absorption and photoluminescence.     

Synthesis,structural analysis and microwave dielectric properties of Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ln<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiTaO<Subscript>6</Subscript> (Ln = Ce,Pr and Nd) Ceramics

Bi substituted LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are prepared using the conventional solid state ceramic route. The materials are calcined at 1,150°C and sintered at 1,375°C. The structure is analysed using X-ray diffraction technique and the microstructure using scanning electron microscopy. The microwave dielectric properties of the samples are measured using the cavity resonator method. Substitution of Bi increases the dielectric constant and improves the thermal stability. A number of samples with improved quality factor are obtained and can be used in practical microwave circuits.     

Dielectric and impedance studies of (Pb<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>)(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> dielectric ceramics

Ceramic samples of (Pb_1?xCa_x)(Fe_0.5Nb_0.5)O₃ with x = 0.20, 0.40, 0.45, 0.50, 0.55 and 0.60 were obtained by columbite precursor method. All the synthesized samples have perovskite structure with pseudo-cubic symmetry. Dielectric properties of all the samples were measured as a function of frequency from room temperature up to 573 K. Two dielectric anomalies were observed in ε_r–T plots at about 400 and 500 K. The impedance analysis depicts a single relaxation process. Activation energies obtained from temperature dependence of relaxation frequency, f₀ and grain resistance, R_g were found to be more or less comparable. The observed relaxation in all the samples seems to be due to electron relaxation associated with oxygen vacancies.     

Novel temperature stable Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>V<Subscript>2</Subscript>O<Subscript>6</Subscript> microwave dielectric ceramics with ultra-low sintering temperature

New temperature stability Ba_1?xSr_xV₂O₆ (0.35?≤?x?≤?0.55) microwave dielectric ceramics prepared by the conventional solid-state route were investigated. X-ray diffraction confirmed that all the specimens formed a solid solution single phase with orthorhombic structure. The microwave dielectric properties strongly depended on the compositions, densification and microstructure of the specimens. Furthermore, partial Sr ions substitution for Ba ions in Ba_1?xSr_xV₂O₆ lattices not only successfully improved the temperature stability of BaV₂O₆-based ceramic but also promoted the sinterability of SrV₂O₆-based one. Out of these compositions, Ba_0.5Sr_0.5V₂O₆ sintered at 625?°C exhibited a near-zero τ_f together with a low permittivity ε_r?~?11.5 and a quality factor Q?×?f?~?14 100 GHz, which also showed good chemical compatibility with Al electrodes.     

Micro-structural,dielectric, ferroelectric and piezoelectric properties of mechanically processed (Pb<Subscript>1−x</Subscript>La<Subscript>x</Subscript>)(Zr<Subscript>0.60</Subscript>Ti<Subscript>0.40</Subscript>)O<Subscript>3</Subscript> ceramics

In this work, (Pb_1?xLa_x)(Zr_0.60Ti_0.40)O₃ (PLZT x/60/40, x?=?at.%) ceramics were prepared by using high energy mechanical ball milling followed by cold isostatic pressing (CIP), investigated for their micro-structural, dielectirc, ferroelectric and piezoelectric properties. Mechanical activation results in the highly reactive nature of the nano size milled PLZT powders, which enables the partial perovskite phase formation, confirmed by room temperature XRD patterns. CIP leads to a higher density with a closely packed dense microstructure of sintered PLZT ceramics shown in SEM images. The grain size of PLZT x/60/40 ceramics was found to be decreasing with increasing La³⁺ content. The highest relative density of ~?97% was found to be for PLZT 8/60/40 ceramics with grain size of ~?1.35 µm. The PLZT 8/60/40 system also shows the highest dielectric constant of ~?1976, remnant polarization of 29.1 µC/cm², piezoelectric coefficients (d₃₃?\(~ \cong ~\)?570 pC/N, g₃₃?\(~ \cong ~\)?28.03?×?10^?3 Vm/N) and electromechanical coupling factors (k_p?=?k₃₃?=?64.1% and k₃₁?=?54%). The elastic compliances for the PLZT x/60/40 ceramics were also obtained.     

Synthesis and properties of columbite-structure Mg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>6 − <Emphasis Type="Italic">x</Emphasis></Subscript>

The formation of the columbite-structure magnesium niobate MgNb₂O₆ is a multistep process. Single-phase material can only be obtained through long-term high-temperature heat treatment. Deviations from stoichiometry have a significant effect on the microwave quality factor Q of the material: magnesium-deficient ceramics contain small amounts of Nb₂O₅ and have relatively low Q values, whereas an excess of magnesium leads to the formation of Mg₄Nb₂O₉ (alpha-alumina structure) as an impurity phase, thereby drastically increasing the electrical Q.     

Preparation,characterization and dielectric properties of Ba<Subscript>3−x</Subscript>Sr<Subscript>x</Subscript>LiM<Subscript>3</Subscript>Ti<Subscript>5</Subscript>O<Subscript>21</Subscript>[M=Nb and Ta,x = 0 to 3] ceramics

The ceramic compositions Ba_3−xSr_xLiM₃Ti₅O₂₁[M=Nb and Ta, x = 0 to 3] were prepared through conventional solid state ceramic route. A detailed study has been carried out to correlate the structure of Ba_3−xSr_xLiM₃Ti₅O₂₁[M=Nb and Ta, x = 0 to 3] with respect to their dielectric properties. The structure and microstructure of ceramic samples were studied using powder X-ray diffractometer and Scanning Electron Microscopic techniques. The dielectric properties of the sintered ceramic compacts have been studied. The Ba-rich compositions were identified as promising candidates for high frequency applications whereas the Sr-rich compositions were excellent ionic conductors and can be commercially exploited for applications in solid-state batteries.     

The crossover of (Ba<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>)(Ti<Subscript>0.9</Subscript>Sn<Subscript>0.1</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics from single-phase to composite with studying the structural and dielectric properties

Lead-free (Ba_1?xCa_x)(Ti_0.9Sn_0.1)O₃ perovskite ceramics (x?=?0.02–0.5) (BCTS) were synthesized using the solid-state reaction technique. X-ray diffraction was used to identify the formed phases of the prepared compositions. The morphology of ceramics has been studied using a scanning electron microscope equipped with an energy dispersive spectrometer. Field emission scanning electron microscope was used to examine the morphology of sensing film calcined powder. The crossover from BCTS single-phase (x?=?0.02) to BCTS composite(x?=?0.5) was obtained via coexistence of both (x?=?0.3) of Ca addition. The composite powder was sintered at higher temperature rather than the single-phase powder. The calcined powder sensing film was prepared by the screen-printing technique as humidity sensors. Thereafter, DC resistance measurements were performed in the presence of relative humidity RH at room temperature. All the compositions exhibited a poor sensitivity toward the humidity sensing in the range of 0–98% RH. The compositions 0.02 and 0.06 have shown orthorhombic–tetragonal phase transition (T_O?T) below the room temperature, while the other compositions have shown a pure tetragonal phase. The highest value of permittivity at Curie temperature (ε?=?29241 at 100 Hz) and piezoelectric coefficient (d₃₃?=?495 pC/N) at room temperature were obtained at Ca?=?0.06 due to present polymorphic phase transition. The effect of frequency on the dielectric constant and dielectric loss at room temperature were investigated. All the prepared compositions exhibited small values of dielectric loss from 50 Hz up to 100 KHz, which indicates a good reliability for electronic applications such as capacitors or memory devices.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.     

Influence of Dy-doping on ferroelectric and dielectric properties in Bi<Subscript>1.05−x</Subscript>Dy<Subscript>x</Subscript>FeO<Subscript>3</Subscript> ceramics

Bi_1.05−xDy_xFeO₃ (BDFO) (x = 0−0.2) ceramics were synthesized by solid-state reaction method. The influence of Dy dopant on crystal structural, dielectric and ferroelectric properties was investigated. The lattice parameter and the Curie temperature of BDFO were degraded continuously with increasing contents of Dy³⁺ cations. Leakage current density, ferroelectric polarization and dielectric loss were improved by appropriate Dy doping. When x = 0.1, BDFO showed the best electric properties. At applied electric field of 53 kV/cm, the remnant polarization (2P _r ) was 12.2 μC/cm².These improvements in electric properties in BDFO ceramics could have resulted from the relatively low oxygen vacancy concentration and structural distortion.     

Electrical and oxygen sensing properties of Nd<Subscript>1−x</Subscript>Ba<Subscript>x</Subscript>CoO<Subscript>3</Subscript> ceramics

Nd_1?xBa_xCoO₃ (0?≤?x?≤?0.2) ceramics was synthesized by solid state reaction. All the samples have an orthorhombic perovskite structure (Space group P n m a). The electrical transport property indicates that Ba doped NdCoO₃ ceramics goes through semiconductor–metal phase transition. The electrical resistivity of Nd_1?xBa_xCoO₃ (0?≤?x?≤?0.15) ceramics decreases, while the electrical resistivity of Nd_0.8Ba_0.2CoO₃ ceramics increases with the increase of temperature. The chemical-sensing property shows that Nd_1?xBa_xCoO₃ ceramics is very sensitive to oxygen. Also, increasing Ba²⁺ doping concentration can reduce the oxygen desorption rate and increase the sensitivity of resistivity. These results indicate that Ba²⁺ doped NdCoO₃ ceramics is not only the good candidate of the cathode materials of solid fuel cells but also the good materials of gas sensor devices.     

Laser and electromagnetic loss properties of Perovskite SmNi<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>O<Subscript>3</Subscript>

SmNi_xFe_1?xO₃ (0?≤?x?≤?0.5) with perovskite-type structure has been successfully prepared by conventional solid-state reaction as a microwave and laser multi-functional material. The optimized synthesis temperature and the effects of Ni doping on the reflectivity, electromagnetic loss properties were investigated in details. XRD results shown that synthesis temperature did not change the perovskite structure of SmFeO₃. The reflectivity at 1.06 μm was about 0.33% at 1200–1300?°C. Doping Ni did not cause the change of perovskite structure. The incorporation of Ni in SmFeO₃ contributed to the decrease of reflectivity at a wider wavelength, SmNi_0.3Fe_0.7O₃ possessed the lowest reflectivity at 1.06 μm. Moreover, electromagnetic property was very sensitive to Ni content. The real and imaginary parts of complex permeability were enhanced remarkably at a certain frequency. The changes in magnetic performance provided possibility of choosing specific frequency of magnetic loss. The difference in electric and magnetic losses caused by Ni concentration could result in microwave absorption at different frequency. In a word, SmNi_xFe_1?xO₃ could be a promising candidate for a multi-functional material with compatible camouflage capability for radar and laser waveband.     

Sintering behaviors and microwave dielectric properties of Ti-modified Ba<Subscript>3</Subscript>Ti<Subscript>5</Subscript>Nb<Subscript>6</Subscript>O<Subscript>28</Subscript> ceramics with 35BaO–35ZnO–30B<Subscript>2</Subscript>O<Subscript>3</Subscript> addition

Effect of 35BaO–35ZnO–30B₂O₃ (BZB) addition on the sintering behaviors, phase evolution and microwave dielectric properties of Ti-modified Ba₃Ti₅Nb₆O₂₈ (Ba₃Ti_5.1Nb_5.9O_27.95, BTNO) ceramics had been investigated. BZB addition effectively reduced the sintering temperature of BTNO from 1250 °C to about 900 °C. With increasing BZB addition, the crystal phase of the present ceramics changed from single phase Ba₃Ti₅Nb₆O₂₈ to mixing phases of Ba₃Ti₅Nb₆O₂₈ and Ba₃Ti₄Nb₄O₂₁. And the major phase gradually became from Ba₃Ti₅Nb₆O₂₈ to Ba₃Ti₄Nb₄O₂₁. Dielectric constant and temperature coefficient increased with the rising of BZB addition. But the Qf value gradually declined from 28000 to about 6000 GHz. The BTNO ceramics with 15% BZB addition exhibited excellent microwave dielectric properties as following: ε?=?46.3, Qf?=?5887 GHz and τ_f?=?35.5 ppm/°C, which was potential of candidate materials for LTCC application. And the variation of microwave dielectric properties had been also discussed with the phase and microstructure evolution.     

Effects on dielectric and magnetic properties of Cr-doped Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>Fe<Subscript>1−x</Subscript>Cr<Subscript>x</Subscript>O<Subscript>3</Subscript> ceramic

In this paper, Cr-doped Bi_0.9Ba_0.1Fe_1?xCr_xO₃ (x = 0.00, 0.05, 0.10, 0.15, 0.20) ceramic materials were prepared by traditional state solid synthesized method, and the effects of Cr³⁺ ion on magnetic and dielectric properties were investigated. All samples showed BiFeO₃ phase formation were successful synthesized. The SEM images showed the shape of samples changed from regular to irregular shape. With increasing of Cr²⁺ ions, Saturation magnetization (M _s) increased from 5.24 to 8.6 emu/g, and then decreased to 7.31 emu/g, and coercivity (H _c) increased from 110.66 to 256.49 Oe. All the samples showed high dielectric constants at low frequency and the values of dielectric constants decreased slightly with frequency increasing. Delectric loss (tanδ) values kept a steady in a wide range frequency of 10–600 MHz. They ranged in tanδ from 0.01 to 0.07, which was a low dielectric loss in Bi_0.9Ba_0.1Fe_1?xCr_xO₃ ceramics.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Microstructure and microwave dielectric properties of (Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>SiO<Subscript>4</Subscript> ceramics

(ZnMg)₂SiO₄ powders was prepared by the sol-gel process, and the microstructure and dielectric properties of (Zn_1−xMg_x)₂SiO₄ microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)₂SiO₄ with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into Zn₂SiO₄ lattice, and the solid solution limit of Mg in Zn₂SiO₄ is about x = 0·1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of Zn₂SiO₄ ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of Zn₂SiO₄. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (Zn_0·8Mg_0·2)₂SiO₄ dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: ɛ _r = 6·3, Q × f = 189800 GHz and τ _f = −63 ppm/°C.     

Chemical,morphological, structural,optical, and magnetic properties of Zn<Subscript>1−x</Subscript>Nd<Subscript>x</Subscript>O nanoparticles

In the present investigation, we made an endeavor to fabricate the ZnO nanoparticles and achieved the tunable properties with Nd doping. The Nd-doped ZnO nanoparticles were characterized via X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies that confirmed the successful doping of Nd ions in the ZnO crystal lattice without amending its hexagonal phase. The particle morphology revealed nearly spherical particles with uniform size distribution. The band gap of these samples was determined using diffuse-reflectance spectra (DRS) and was found to vary from 3.17 to 3.21 eV with increasing Nd concentration. A broad and intense emission band at 1083 nm for Nd doped ZnO nanoparticles is observed and is assigned to corresponding emission transition ⁴F_3/2?→?⁴I_11/2 of Nd³⁺ ions. Furthermore, the magnetic studies indicate that the Nd doping altered the magnetic behavior of nanocrystalline ZnO particles from diamagnetic to ferromagnetic at 300 K and that the magnetization of these samples decreased with increasing Nd concentration. The tunable optical band gap as well as room-temperature ferromagnetism of these samples may find applications in both optoelectronics and spintronics.     

Microwave dielectric properties of Ba<Subscript>4</Subscript>LaTiNb<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Ta<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>15</Subscript> ceramics

High dielectric constant and low loss ceramics in the system Ba₄LaTiNb_3−x Ta _x O₁₅ (x = 0–3) have been prepared by conventional solid-state ceramic route. Ba₄LaTiNb_3−x Ta _x O₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 53.1 to 42.3, quality factor Q_u × f from 18,790 to 28,070 GHz and temperature variation of resonant frequency from +94.3 to +33.1 ppm/°C as the value of x increases.     

Electrical properties of B site substituted (K<Subscript>0.48</Subscript>Na<Subscript>0.52</Subscript>)(W<Subscript>2/3</Subscript>Bi<Subscript>1/3</Subscript>)<Subscript>x</Subscript>Nb<Subscript>1−x</Subscript>O<Subscript>3</Subscript> piezoceramics

Lead-free (K_0.48Na_0.52)(W_2/3Bi_1/3)_xNb_1−xO₃ (KNN-WBi) piezoceramics with x ranging from 0.004 to 0.010 were synthesized by conventional ceramic processing. The sintered KNN-WBi ceramics showed perovskite structure without detectable secondary phase containing W and Bi. With increasing x, the orthorhombic-tetragonal phase transition temperature (T _O-T) decreased from 200 to 184 °C whereas, the tetragonal-cubic phase transition temperature (T _C) decreased slightly. With the doping of (W_2/3Bi_1/3), the piezoelectric properties were greatly improved and the piezoelectric constants d ₃₃, k _p, Q _m exhibited maximum values of 136 pC/N, 43.3% and 175, respectively at x = 0.008. The KNN-WBi ceramics also exhibited good ferroelectric properties with remnant polarizations P _r higher than 25 μC/cm² and coercive fields E _c lower than 1,000 V/mm. The results strongly suggest that the B site doping of constructed quinquevalent element is an effective method for the investigation of potassium sodium niobate system.