Crystal structures and microwave dielectric properties of low-firing Ca5Zn4-xMgxV6O24 ceramics

Ca₅Zn_4-xMg_xV₆O₂₄ (x?=?0–3) microwave dielectric ceramics with low sintering temperature were synthesized via the conventional solid-state reaction. Effects of the substitution of Mg²⁺ for Zn²⁺ on crystal structures and microwave dielectric properties were investigated. XRD and Rietveld refinement showed the solid solution single phase formed when 0?≤?x?≤?2, but a few ZnO was observed when x?=?3. Meanwhile, the lattice parameters were found to decrease monotonously with Mg content increasing. The vibration modes of Raman were confirmed and the relationship with microwave dielectric properties was analyzed. Appropriate substitution of Mg²⁺ improved the packing fraction, the cation ordering degree, and the Y-site bond valence, contributing to high Q×f and low | τ_f |. However, the ε_r reduced with the increasing content of Mg²⁺ due to the decrease of ion polarizability. Finally, the best microwave dielectric properties were achieved at x?=?2 with ε_r =?11.0, Q?×?f?=?66,365?GHz (at 10.0?GHz), and τ_f =??80.4?ppm/°C.     

Higher permittivity of Ni-doped lead zirconate titanate,Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics

The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr_0.52Ti_0.48)O₃] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0–20?at%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT ceramic samples which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597?cm^?1, 608?cm^?1, 611?cm^?1, 605 and 613?cm^?1 for Ni?=?0, 5, 10, 15 and 20?at%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε′) & tanδ as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni?=?5?at%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (ε′_max) decreased while the phase transition temperature increased with increase in doping concentration of Ni. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068?eV for x?=?0.00 to x?=?0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.     

Microwave absorption properties of CoGd substituted ZnFe2O4 ferrites synthesized by co-precipitation technique

A series of co-precipitated Zn_1?xCo_xGd_yFe_2?yO₄ spinel ferrites (x = 0.0–0.5, y = 0.00–0.10) sintered at 1000 °C were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometery (VSM) and microwave cavity perturbation (MCP). XRD patterns and FTIR spectra reveal formation of the spinel phase along with few traces of GdFeO₃ second phase. The lattice constant decreases with an increasing amount of CoGd ions due to the segregation of Gd³⁺on the grain boundaries and due to replacement of lager Zn²⁺ ions with smaller Co²⁺ ions. SEM shows grain size to decrease with the increase of CoGd contents due to grain growth inhibition by the second phase. VSM results show remanence and saturation magnetization to exhibit an increasing trend due to Co substitution on octahedral sites and presence of a second phase. The coercivity increases with the increase of CoGd contents due to anisotropic nature of Co. MCP shows the complex magnetic permeability to increase with CoGd concentration while the complex permittivity decreases.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

MgO-modified Sr0.7Ba0.3Nb2O6 ceramics for energy storage applications

We explored the phase structure, microstructure, dielectric and energy storage properties of MgO-modified strontium barium niobate Sr_0.7Ba_0.3Nb₂O₆-xwt%MgO (SBNMx; x?=?0–5) ceramics fabricated via conventional solid-state sintering precess. X-ray diffraction analysis indicates Mg²⁺ incorporates into lattice at x?=?0.5 and secondary phases come into formation for samples at x?≥?1, which results in the decrease of dielectric constant. There is also significant reduction of dielectric loss up to 0.002. Compared with pure SBN ceramics, the grain size of SBNMx ceramics becomes denser and more uniform, moreover, the dielectric breakdown strength shows increasing trend from 137?kV/cm to 226?kV/cm, which is in favor of the energy storage. SBNM0.5 ceramics presents the optimal energy storage performance: energy storage density of 0.93?J/cm³ and energy storage efficiency of 89.4% at 157?kV/cm, indicating that SBNM ceramics are prospective candidates for high voltage capacitor applications.     

Frequency, temperature and In dependent electrical conduction in NiFe2O4 powder

A series of polycrystalline spinel ferrites with the composition NiIn_xFe_2-xO₄ (0 ≤ x ≤ 0.3) were prepared by the solid state reaction to study the effect of In³⁺ ions substitution on their dc electrical resistivity and dielectric properties. The dc resistivity has been investigated as a function of temperature and composition. The indium ion increases the dc resistivity and activation energy of the system. A study of the dielectric properties of these mixed ferrites, as a function of composition, frequency and temperature, has been undertaken. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) all decreases with frequency as well as with the composition. The dielectric constant (ε′) and dielectric loss tangent (tanδ) were increases with increasing temperature. AC conductivity increases with increase in applied frequency. The dielectric behavior of the present samples is attributed to the Maxwell-Wagner type interfacial polarization. The conduction mechanism in these ferrites is due to electron hopping between Fe²⁺ and Fe³⁺ ions on adjacent octahedral sites.     

Effects of structural characteristics on microwave dielectric properties of low-loss (Zn1-xNix)ZrNbTaO8 ceramics

Low-loss (Zn_1-xNi_x)ZrNbTaO₈ (0.02?≤?x?≤?0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni²⁺ (x?=?0.06) in A-site with the fixed substitution of Ta⁵⁺ in B-site can effectually raise the Q?×?f value of ZnZrNb₂O₈ ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ_f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn_0.94Ni_0.06)ZrNbTaO₈ ceramic sample sintered at 1150?°C for 3?h exhibits an outstanding combination of microwave dielectric properties: ε_r =?27.88, Q?×?f?=?128,951?GHz, τ_f =?–39.9?ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency.     

Tuning of Bi3+-related excitation and emission positions through crystal field modulation in the perovskite-structured La2(Znx, Mg1-x)TiO6 (0 ≤ x ≤ 1):Bi3+ solid solution for white LEDs

In the past year, emission-tunable crystals based on the rare-earth (RE) ions as luminescent center have been frequently reported for use in UV and blue converted white LEDs, but so far tuning the non-RE Bi³⁺ related emissions through the crystal field modulation is still not discovered in the perovskite crystals. In this work, we design and report a type of Bi³⁺ doped La₂(Zn_x,Mg_1-x)TiO₆ (0 ≤ x ≤ 1) perovskite solid solutions, which enable showing the tunable Bi³⁺ excitation and emission positions. The XRD results show that gradual substitution of smaller Mg²⁺ ions with larger Zn²⁺ ions can lead to the blue-shifting of X-ray diffraction (XRD) position, revealing the expansion of cell lattice. Together with structural analysis, our refined XRD and time-resolved spectral results reveal that there is only one type of La site available for Bi³⁺ substitution. With this regular crystal lattice change, the crystal field strength around Bi³⁺ ions is found to vary regularly, allowing to realization of the excitation and emission spectral tuning, i.e., the Bi³⁺ excitation and emission positions as the Mg ions are replaced by the Zn ions can tune from 348?nm to 392?nm and from 405?nm to 433?nm, respectively. This Bi³⁺ spectral tuning peak after calculated by the dielectric chemical bond theory features a linear relationship with the crystal field strength and, thus, is ascribed to the crystal field modulation. On basis of the La₂(Zn_0.4,Mg_0.6)TiO₆ blue, SrGa₂S₄:Eu²⁺ green and Y₂O₃:Eu³⁺ red phosphors, a UV converted warm white LED device with desirable color rendering index (CRI) of 78, correlated color temperature (CCT) of 3650 K and good luminous efficacy of 118.13?lm/W, is fabricated. This work provides new insights into using the crystal-field modulation to discover more Bi³⁺ emission-tunable crystals for white LEDs in the future.     

Erbium substituted nickel–cobalt spinel ferrite nanoparticles: Tailoring the structural,magnetic and electrical parameters

In this article, we have reported an effective, rapid as well as economical Er³⁺ substituted Ni_0.4Co_0.6Fe₂O₄ ferrite nanoparticles synthesized via surfactant-assisted co-precipitation route. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), dielectric properties, current-voltage (I–V) measurements, and vibrating sample magnetometry (VSM). XRD and FTIR confirmed the face-centered (FCC) spinel structure of all compositions of the synthesized spinel ferrite nanoparticles. The deviations in the lattice constant granted with the variation in size of the guest (Er³⁺) and host (Fe³⁺) cations. These ferrites were also subjected for electrical, magnetic and dielectric investigations. I–V measurements showed that resistivity values decreased from 6.20 × 10⁷ Ω cm to 0.03 × 10⁷ Ω cm with the increased Er³⁺ contents. Saturation magnetization increased from 35.99 to 39.95 emu/g. This high value of saturation magnetization suggested the possible utilization of such ferrites for practical applications such as microwave and recording devices fabrication. Interestingly, the magnetic and dielectric properties of nickel-cobalt ferrite nanoparticles showed ample improvement upon Er³⁺ substitution. The results clearly indicate the potential of Er⁺³ substituted spinel ferrite particles in various advanced technological devices fabrication.     

Crystal structure,microwave dielectric properties and low temperature sintering of (Al0.5Nb0.5)4+ co-substitution for Ti4+ of LiNb0.6Ti0.5O3 ceramics

The phase composition, microstructure, microwave dielectric properties of (Al_0.5Nb_0.5)⁴⁺ co-substitution for Ti site in LiNb_0.6Ti_0.5O₃ ceramics and the low temperature sintering behaviors of Li₂O-B₂O₃-SiO₂ (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li_1.075Nb_0.625Ti_0.45O₃ solid solution was formed in all component. The increase of dielectric constant (ε_r) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τ_f value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb_0.6Ti_(0.5-x)(Al_0.5Nb_0.5)_xO₃ ceramics (x?=?0.10) when sintered at 1100?℃ for 2?h: ε_r =?70.34, Q×f =?5144?GHz, τ_f =?4.8?ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x?=?0.10 were obtained with 1.0?wt% glass: ε_r =?70.16, Q×f =?4153?GHz (at 4?GHz), τ_f =?-0.65?ppm/℃ when sintered at 925?℃ for 2?h.     

Electric and dielectric study of cobalt substituted MgMn nanoferrites synthesized by solution combustion technique

Cobalt substituted Mg–Mn nanoferrites with formulae Mg_0.9Mn_0.1Co_xFe_2?xO₄, x=0.0, 0.1, 0.2 and 0.3, have been synthesized for the first time by the solution combustion technique. The effects of Co²⁺ ions on the dc resistivity, dielectric constant and dielectric loss tangent of Mg–Mn nanoferrites at room temperature are presented in this paper. X-ray diffraction confirmed the formation of a single phase spinel structure. Particle size was found to increase, 20.9–23.9 nm, with increasing Co²⁺ concentration. The dc resistivity was increased by two order of magnitude with substitution of Co²⁺ ions while the dielectric constant was found to be decreasing with the increasing concentration of cobalt ions. The value of dc resistivity obtained for Mg_0.9Mn_0.1Fe₂O₄ nanoferrite in our work is greater than the value obtained for the same composition prepared by the conventional ceramic technique. Further, the dielectric constant and dielectric loss tangent were observed to be decreasing with the increase in frequency.     

Influence of rare-earth La3+ ion doping on microstructural,magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La³⁺ ion doped magnesium nickel ferrites, Mg_0.5Ni_0.5Fe_2-xLa_xO₄ (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La³⁺ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La³⁺ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La³⁺ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La³⁺ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.     

Infiltrated La0.5Ba0.5CoO3-δ in La0.8Sr0.2Ga0.8Mg0.2O2.8 scaffolds as cathode material for IT-SOFC

The electrochemical response of infiltrated La_0.5Ba_0.5CoO_3-δ (LBC) in porous La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 (LSGM) has been investigated. The thermal expansion coefficient (TEC) of the resulting electrode was measured, obtaining α?=?12.5?×?10^?6 K^?1, a value similar to that of LSGM. The polarization resistance (Rp) and the processes involved in the oxygen reduction reaction (ORR) for the new electrode were studied and analyzed through complex impedance spectroscopy measurements as a function of temperature and oxygen partial pressure (pO₂), using a symmetrical cell. The value of Rp for the infiltrated LBC turned out to be lower than that measured for an electrode prepared with a composite LBC-LSGM (1:1?wt%) by an order of magnitude, for the temperature range 750?°C ≤ T?≤?900?°C, and about 5 times lower for the temperature range 450?°C≤ T?≤?650?°C. At 600?°C, the LBC infiltrated cathode exhibits a polarization resistance R_p =?0.22?Ω?cm², in air. The complex impedance spectra show two processes, one identified as low frequency (LF),with a characteristic frequency of 10?Hz, and the other as intermediate frequency (IF), with a range between 0.05 and 2000?Hz. The LF process could be associated to the diffusion of oxygen in the gas phase through the pores of the electrode. Its resistance, R_LF =?0.01?Ωc?m²_, was found to be independent of the temperature and half of that obtained for the LBC composite cathode. On the other hand, the IF process is related to charge transfer at the electrode surface and the electrode-electrolyte interface. The LBC cobaltite infiltrated in the LSGM scaffolds offers an adequate thermal expansion coefficient and good electrocatalytic activity for the ORR.     

Significant reduction of dielectric loss of Ba0.51Sr0.34TiO3 film modified by Y/Mn alternate doping and preheating

To achieve significant reduction of dielectric loss and enhancement of dielectric tunability for actual applications, a Ba_0.51Sr_0.34TiO₃ film modified by Y/Mn alternate doping (Y/Mn-BST_0.85) is prepared by an improved sol-gel method, where the film is composed of 12 layers, and odd number layers are preheated. For comparison, BST_0.85, Y-BST_0.85 and Mn-BST_0.85 films are also prepared. XRD shows four films are ABO₃ cubic perovskite structures. The BST_0.85 film shows the smallest lattice parameter and donor doping because rich Ti⁴⁺ ions enter into A sites to replace some Sr²⁺ and Ba²⁺ ions. Besides the donor doping, three doped BST_0.85 films exhibit slightly larger lattice parameters and acceptor doping because Y³⁺ or Mn²⁺ ions replace some Ti⁴⁺ ions at A sites. The Y/Mn-BST_0.85 film shows the largest lattice parameter and the strongest crystallinity because Y-BST_0.85 layer and Mn-BST_0.85 layer match well in lattice structure. Compared to stoichiometric films, four nonstoichiometric films show markedly decreased dielectric losses. The Y/Mn-BST_0.85 film exhibits the lowest dielectric loss with 0.45 ~ 0.54% under the conditions of ??40 to 40V and 100?kHz, and 0.43 ~ 2.29% under the conditions of 10?Hz ~ 1?GHz and 0?V, thus can satisfy actual applications including tunable microwave application at high frequencies. The related mechanisms are studied by measuring leakage current density, observing AFM and analyzing XPS besides analyzing the XRD patterns.     

Observation of efficient Er3+:4I11/2→4I13/2 transition in highly Er3+ doped germanosilicate glass

Highly rare earth（RE）ions doped glass laser materials can produce efficient single frequency mid-infrared laser. In this work, a series germanosilicate glasses with various high erbium-doping concentration (up to 4?mol%) and without concentration quenching are fabricated. Spectroscopic properties and energy transfer (ET) mechanism of efficient Er³⁺:⁴I_11/2 →⁴I_13/2 transition have been investigated in detail upon a conventional 980?nm Laser Diode. The dense structure of silicate glass can be dissolved effectively by the introduction of GeO_2, which was analyzed by Raman spectra, so that the compatibility and luminous intensity of RE ions were improved. The high predicted spontaneous transition probability (A_rad =?37.65?s^?1) based on the Judd-Ofelt theory and large calculated emission cross section (8.8?×?10^?21 cm²) are obtained. The above results indicate that these glasses are promising to be the single frequency mid-infrared laser material.     

Synthesis of MFe2O4 (M=Mg2+, Zn2+, Mn2+) spinel ferrites and their structural,elastic and electron magnetic resonance properties

Structural, elastic and electron magnetic resonance investigations of spinel ferrites with the formula MFe₂O₄ (M = Mg²⁺, Zn²⁺, Mn²⁺) synthesized by the sol-gel auto-combustion method are reported here. XRD patterns revealed the co-existence of secondary phases along with the ferrite phase. The lattice parameter (8.301?Å, 8.366?Å and 8.434?Å) was found to be varying according to the ionic radii of cations. As determined by scanning electron microscopy (SEM), ZnFe₂O₄ has a comparatively narrow distribution of grain sizes (1.3–3.8?µm) compared to those in MnFe₂O₄ (0.8–4.3?µm) and MgFe₂O₄ (0.3–4.8?µm). The estimated values of average crystallite sizes (17.5?nm, 21.3?nm and 23.3?nm) determined from the X-ray diffraction peaks are considerably less than the average grain sizes (1.3?µm, 1.6?µm and 2.7?µm) estimated from the SEM histograms. The vibrational frequencies in FTIR spectra are in the conformity with the cubic spinel structure and their variation supports the variation of lattice parameter. Equal values of Poission's ratio (0.35) were obtained for the three systems which represent the isotropic behaviour of spinel ferrite systems. The exceptional low value of Lande's g-parameter for ZnFe₂O₄ indicates the dominance of Fe³⁺–O–Fe³⁺ superexchange interaction. Though cation redistribution is possible in the present ferrite systems, the secondary phases existed in these ferrite systems are predominantly influencing the structural, elastic and electron magnetic resonance properties.     

The influence of Zr and Ni co-substitution on structural,dielectric and magnetic traits of lithium spinel ferrites

The impact of Ni²⁺ and Zr⁴⁺ on the physical properties of LiFe₂O₄ ferrites is investigated and synthesized via the microemulsion technique. X-ray diffraction pattern of pure and substituted lithium ferrites exhibited spinel structure. The constant lattice increases with increasing dopants concentration up to x = 0.2 and decreases for higher x. The crystallite size value varies from 8.15 to 12.37 nm. The incorporation of heavier ions with lighter ions increased the X-ray density of lithium ferrites. The value of dielectric parameters such as dielectric constant and dielectric loss decreases with the substation of Ni²⁺ and Zr⁴⁺ ions. The Maxwell Wagner model ascribes the decrease in dielectric parameters. Substituted lithium ferrites observe a high Q value. The magnetic studies revealed that saturation magnetization and coercivity were significantly affected by Ni²⁺ and Zr⁴⁺ ions. The inclusion of Ni²⁺ and Zr⁴⁺ ions improves the dielectric and magnetic properties making it suitable for high-frequency applications.     

Structural and functional properties of sol-gel synthesized and microwave heated Pb0.8 Co0.2-zLazTiO3 (z = 0.05–0.2) nanoparticles

The present work reports the effect of La-substitution on structural and functional properties of lead cobalt titanate (PCT) perovskite structure as a function of variation of Co-content. The sol-gel synthesized and microwave heated Pb_0.8 Co_0.2-zLa_zTiO₃ (z?=?0.05, 0.1, 0.15 & 0.2) (PCLT) nanoparticles showed the presence of complete cubic phases while few were noted to be tetragonal lead titanate (PT) phases. The surface morphology was examined by field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). The HRTEM revealed fibers like nanoparticles at z?=?0.15 and 0.2. The Fourier transform infrared spectra attributed the presence of metal oxide bonds. Furthermore, the wide optical band gap energy (E_op) was acquired to be changing from 2.32 to 3.20?eV. In addition, the electrical parameters such as dielectric constant (ε'), dielectric loss (ε"), ac & dc-electrical conductivity (σ_ac & σ_dc), complex dielectric modulus (M^*) and complex impedance (Z^*) were studied as a function of frequency (f) and composition. Using power law fitting, the σ_dc values were determined. The z?=?0.15 content exhibited high σ_dc of ~ 2.51?×?10^?7 S/cm among all compositions. Besides, the results expressed the existence of short range and long range hopping conduction regions in dielectric modulus spectra. The Nyquist plots were drawn to elucidate the electrical conduction and relaxation mechanism. Later on, ferroelectric hysteresis loops were recorded for z?=?0.05–0.2.     

Correlations between the structural characteristics and enhanced microwave dielectric properties of V–modified Li3Mg2NbO6 ceramics

Novel low-temperature fired Li₃Mg₂Nb_1-xV_xO₆ (x?=?0.02??0.08) microwave dielectric ceramics were synthetized by the partial substitution of V⁵⁺ ions on the Nb⁵⁺ sites. The effects of V⁵⁺ substitution on structure and microwave dielectric properties were investigated in detail. XRD patterns and Rietveld refinement demonstrated that all of the samples exhibited a single orthorhombic structure. The structural characteristics such as the polarizability, packing fraction and NbO₆ octahedron distortion were determined to establish the correlations between the structure and the microwave dielectric characteristics. The ?_r values presented a tendency similar to that of the polarizability. The high Q×f values were mainly attributed to the effects of the grain sizes and density rather than the packing fraction. The variation in the τ_f values was attributed to NbO₆ octahedron distortion. Notably, the Li₃Mg₂Nb_1-xV_xO₆ (x?=?0.02) ceramics sintered at 900?°C had outstanding microwave dielectric properties: ε_r=?16, Q×f=?131,000?GHz (9.63?GHz), and τ_f=???26?ppm/°C, making these ceramics promising ultralow loss candidates for low temperature co-fired ceramics (LTCC) applications.     

Reduced dielectric loss and high piezoelectric constant in Ce and Mn co-doped BiScO3-PbCexTi1-xO3-Bi(Zn0.5Ti0.5)O3 ceramics

MnO₂-doped 0.99(0.36BiScO₃-0.64PbTi_1-xCe_xO₃)-0.01Bi(Zn_0.5Ti_0.5)O₃ (BS-PTC-BZT-MnO₂) ceramics are fabricated by the solid-state method. Here, it's firstly reported that Ce element can reduce dielectric loss (tan δ) and suppress the decrease of piezoelectric constant (d₃₃) simultaneously. Effects of Ce contents on the structure and electrical properties of BS-PTC-BZT-MnO₂ ceramics are studied. The ceramics (x?=?0.02) with MPB (rhombohedral-tetragonal) possess low dielectric loss (tan δ?=?1.36%, 1?kHz) and high piezoelectric constant (d₃₃ =?360 pC/N) simultaneously, which is superior to most reported BS-PT. Besides, excellent comprehensive properties including high Curie temperature (T_C =?422?°C), large dielectric constant (?_r =?1324), and high remnant polarization (P_r =?35.1?µC/cm²) are obtained. Asymmetric S-E and P-E hysteresis loops indicate that defects and oxygen vacancies are induced by multi-valence elements (Ce and Mn), which is the origin for reducing tan δ. In addition, good thermal stability of piezoelectric and dielectric properties is observed. These results indicate that Ce and Mn co-doped BS-PTC-BZT-MnO₂ ceramics can be well applied as power electronic devices under high temperature.