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Abstract: The optical properties and microwave dielectric properties of transparent polycrystalline MgAl2O4 ceramics sintered by spark plasma sintering (SPS) through homemade nanosized MgAl2O4 powders at temperatures between 1250°C and 1375°C are discussed. The results indicate that, with increasing sintering temperatures, grain growth and densification occurred up to 1275°C, and above 1350°C, rapid grain and pore growth occurred. The in-line light transmission increases with the densification and decreases with the grain/pore growth, which can be as high as 70% at the wavelength of 550nm and 82% at the wavelength of 2000nm, respectively. As the sintering temperature increases, Q×f and dielectric constant ε r values increase to maximum and then decrease respectively, while τ f value is almost independent of the sintering temperatures and remains between −77 and −71ppm/°C. The optimal microwave dielectric properties (ε r=8.38, Q×f=54,000GHz and τ f=−74ppm/°C) are achieved for transparent MgAl2O4 ceramics produced by spark plasma sintering at 1325°C for 20min. [Copyright &y& Elsevier]

Abstract: Approximately 400nm grain sized boron–carbon ceramic was synthesized by the pulsed electric current sintering (PECS) method using boron and carbon powders. Relative density of up to 95% was achieved at sintering temperature of 1900°C. This ceramic was composed with B13C2 as major phase and few B4C and C, which were characterized by X-ray diffraction (XRD) and Rietveld refinement quantitative analysis and chemical analysis (CA) and electron probe microanalysis (EPMA). The microstructure was also observed via transmission electron microscope (TEM). [Copyright &y& Elsevier]

Abstract: The structure, dielectric properties and phase transition of lithium and potassium modified Bi0.5Na0.5TiO3 ceramics were investigated widely. The phase transition behavior with respect to changes in composition and temperature was investigated using X-ray diffraction analysis, dielectric and ferroelectric characterizations. The experimental results show that there is a diffusion phase transition in (Na1−x K x )0.5Bi0.5TiO3 ceramics at T m and the diffuseness of the phase transition is more obvious for the samples near the morphotropic phase boundary. In (Na1−x Li x )0.5Bi0.5TiO3 system, due to the space charge polarization induced by ions conductivity, the low frequency permittivity increases so remarkably at high temperature that the peak of maximum permittivity vanishes. The hysteresis loops at different temperatures indicate that there is no existence of anti-ferroelectrics in lithium and potassium modified Bi0.5Na0.5TiO3 ceramics above the depolarization temperature T d. The depolarization reason is that the tetragonal nonpolar phase occurs and leads to the macro–micro domain transformation at about T d. [ABSTRACT FROM AUTHOR]

Abstract: The effects of SrTiO3 additives on the microstructure and the dielectric properties of Ba4.2Sm9.2Ti18O54 (BST) materials have been investigated. The microstructure of BST doped with SrTiO3 was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The XRD, SEM and EPMA results showed that small amounts of SrTiO3 (less than 4wt.%) could be accommodated in BST while a secondary metatitanate phase appeared in the samples with 8wt.% SrTiO3 added, the addition of SrTiO3 increased the lower solubility limit (x values) of Ba6−3x Sm8+2x Ti18O54. The relative permittivities and the TCf values showed an approximately linear increase with increasing additions of SrTiO3. It was observed that near zero TCf values could be achieved with the addition of SrTiO3 to BST ceramics. With 4wt.% SrTiO3 addition and sintered at 1360°C for 2h, BST ceramics exhibited excellent dielectric properties: ɛ r =81.2, Q f =8470GHz and TCf =−1.5ppm/°C. [Copyright &y& Elsevier]

Abstract: Influence of La2O3 additions on the microwave dielectric properties of Ba0.6Sr0.4TiO3 (BST) mixed with magnesium oxide () composites was investigated. With increasing quantities of lanthanum oxide x (wt%), the lattice constant of BST–MgO material decreases to a minimum at x =0.4 and then increases up to a maximum at x =1.0. The XRD patterns analysis reveal that the solubility of MgO in BST is influenced by the amount of La2O3 doping. SEM observations show that the BST grain sizes decrease with increasing amounts of La2O3. The dielectric properties of BST–MgO–La2O3 indicate that La2O3 additives shift the Curie point towards lower temperatures. Optimum doping amount of La2O3 can reduce the high frequency loss tangents of BST–MgO compound which also can ensure the moderate dielectric constant and tunability. Excessive doping of La2O3 tends to significantly lower dielectric constant and deteriorate tunability. When the doping amount of La2O3 is 0.2wt%, BST–MgO composite has the following properties: dielectric constant=94.05, tan δ =0.012 (at 2.853GHz) and the dielectric constant tunability=16.26% (under electric field 3.57kV/mm), which is suitable for ferroelectric phase shifter. [Copyright &y& Elsevier]

Abstract: The stoichiometry of B–C thin films was controlled via pulsed laser deposition using a series of ceramic B–C targets (B/C ratio was 3.04–5.92). The effects of B/C ratio in target, laser power and substrate-to-target distance on deposition rate, microstructure, stoichiometry and chemical structure were investigated. The maximum deposition rate was obtained at laser power of 90mJ and substrate-to-target distance of 50mm. Boron rich B–C films were obtained and the stoichiometry in B–C thin films was controlled in the range 2.9–4.6. Carbon atoms were bonded with only sp3 hybridization when boron was rich,but with sp2 and sp3 hybridizations when carbon was rich. [Copyright &y& Elsevier]

Abstract: Li2ZnTi3O8 ceramics doped with ZnO–B2O3 frit were prepared by the conventional solid-state reaction. The effects of the ZnO–B2O3 frit on the sintering characteristic, phase composition, microstructure and microwave dielectric properties of Li2ZnTi3O8 ceramics were investigated. A single-phase Li2ZnTi3O8 is formed and no secondary phase is found in the XRD patterns. It is also found that ZnO–B2O3 frit can lower the sintering temperature of the ceramics by about 200°C without seriously deteriorating the microwave dielectric properties. Typically, the ceramics doped with 0.25wt.% ZnO–B2O3 frit sintered at 950°C show good microwave dielectric properties of εr =25.34, Q×f=61,660GHz, and τf =−12.98ppm/°C. [Copyright &y& Elsevier]

Abstract: B13C2 boron carbide ceramic was prepared by pulsed electric current sintering from raw element boron and graphite powders. The planar defects in (104) planes were investigated by transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed the B12 C–B–C configuration of B13C2 ceramic agreed well with C1s spectra measurement. The weakly linked C–B–C chains made the atomic disorder in (104) planes which led to defects in these planes. [Copyright &y& Elsevier]

Porous SiC film is an excellent electrode material for robust micro-supercapacitors used in extremely harsh environments. In one of our previous studies, porous 3C–SiC film with high areal capacitance and high deposition rate was prepared via laser chemical vapor deposition (LCVD). However, it is still urgent to explore the formation mechanism of porous structures using LCVD. In this study, the microstructure of the porous cubic SiC film prepared via LCVD was analyzed in detail using scanning and transmission electron microscopy techniques. The growth mechanism of the deposits has been proposed according to the "growth competing theory" and "shadow effect theory." [ABSTRACT FROM AUTHOR]

A novel microwave dielectric ceramic of SrGa 2 Si 2 O 8 was synthesized using the traditional solid-state method. Its phase composition, microstructure, and microwave dielectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and network analyzer. XRD results indicated that the space group of the ceramic transformed from I 2 /c to P 21 /a at 700 °C. A combination of good microwave dielectric properties was obtained at 1260 °C with ε r = 6.3, Q × f= 96,600 GHz and τ f = −45.2 ppm/°C at 16.5 GHz. The negative τ f can be tuned to near zero by adding 15 mol% CaTiO 3. The densification temperature can be reduced to 940 °C by adding 4 wt% LiF. Moreover, the SrGa 2 Si 2 O 8 ceramic had good chemical compatibility with the Ag electrode. A patch antenna was designed using the 0.85SrGa 2 Si 2 O 8 + 0.15CaTiO 3 + 4 wt% LiF ceramic. The antenna had a high radiation efficiency of 99.2 % and a gain of 2.988 dBi at the center frequency of 4.261 GHz. All results indicated that the SrGa 2 Si 2 O 8 ceramic has promising potential for applications in 5 G wireless communication technology. [ABSTRACT FROM AUTHOR]

BiFeO 3 -based lead-free ferroelectric is considered a potential candidate for energy storage applications owing to its high spontaneous polarization. To tackle the compromise between high polarization and energy storage density, NaNbO 3 (NN) was introduced into 0.7BiFeO 3 -0.3Ba(Hf 0.05 Ti 0.95)O 3 (BF-BHfT) ceramics, where Nb5+ ions enter the BF-BHfT lattices and enhance resistivity, while Na+ ions occupied on the A-sites and smash the long-range ferroelectric order into polar nanoregions. Consequently, the ceramics could maintain high maximum polarization and low remanent polarization. High recoverable energy density (W rec) of 5.2 J/cm3 and efficiency (88%) were recorded in 0.53BF-0.3BHfT-0.17NN ceramics. Besides, it exhibited good thermostability up to 120 °C (W rec variation < 5%), frequency stability from 10 to 200 Hz (W rec variation < 7%) and excellent fatigue resistance after 104 cycles (W rec variation < 0.2%). Under different electric fields the efficiency still maintains nearly constant. In charge-discharge test a W dis of 3.7 J/cm3 was recorded, which proved 0.53BF-0.3BHfT-0.17NN ceramics a promising candidate for energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel high-efficiency dielectric patch antenna was fabricated using Sr 3- x Ca x V 2 O 8 ceramics. A typically temperature-stable Sr 3- x Ca x V 2 O 8 was achieved by tailoring the Ca2+ substitution to 30 mol% (x = 0.3), where well-balanced microwave dielectric properties were obtained (a near-zero value of +5.2 ppm/°C, a low ε r ∼ 13.4, and a moderate Q × f ∼ 18,500 GHz). To manifest the application potentiality in wireless communication, a patch antenna was fabricated from the x = 0.3 ceramic based on the simulated result using the CST Microwave Studio software, and it showed a high simulated radiation efficiency (99.7%) and a gain (5.35 dBi) at 3.421 GHz. All results indicate that the Sr 3- x Ca x V 2 O 8 ceramics have promising application potential for 5 G technology due to their prominent microwave dielectric properties, lightweight, and low cost. [ABSTRACT FROM AUTHOR]

Not only the optical properties, but the microwave dielectric properties of Yttrium aluminium garnet (Y 3 Al 5 O 12 , YAG) ceramics prepared by co-precipitation method combined with spark-plasma sintering (SPS) were investigated by means of adjusting the factors of LiF additive, Nd dopant, and SPS process parameters. Results showed that the in-line transmittance of YAG ceramic with LiF sintered at 1360 °C was 81.8% in the infrared range. With increased sintering temperature, the quality factor (Q × f) and dielectric constant (ε r ) values of the pure YAG ceramics increased to the maximum and then decreased. The optimal microwave dielectric properties (Q × f = 89,810 GHz, ε r = 10.63 and τ f = −51.4 ppm/°C) are achieved for transparent YAG ceramics sintered at 1360 °C. The Q × f values of Nd:YAG ceramics were lower than those of the pure YAG ceramics. The optimal microwave dielectric properties of 2 at.%Nd:YAG ceramic cylinder can be obtained with the Q × f of 64,026 GHz, ε r of 10.2 and τ f of −64.8 ppm/ °C. [ABSTRACT FROM AUTHOR]

High-speed signal propagation systems require dielectric ceramics with low relative permittivity (ε r) and a high-quality factor (Qxf). In this paper, a novel low-permittivity borate ceramic (LiBO 2) was synthesized using a conventional solid-state reaction method. Based on the X-ray diffraction and Rietveld refinement, the LiBO 2 crystallized into a monoclinic structure with a space group of P21/c. Dense and single-phase ceramic was obtained at 640 °C with comprehensive microwave dielectric properties: a low relative permittivity (ε r) of 5.3, a moderate quality factor (Q × f) of 18,200 GHz at 16.3 GHz, and a temperature coefficient of resonant frequency (τ f) of − 66.2 ppm/°C. Good chemical compatibility with Ag electrode and thermal expansion coefficient of 25.4 ppm/°C was achieved demonstrating the potential applications as dielectric resonances in wireless communications and substrates in low-temperature cofired ceramics. [ABSTRACT FROM AUTHOR]

The 0.7Bi 1.05 FeO 3 -0.3BaHf x Ti (1− x) O 3 (BF-BHT- x) ceramics are prepared by using conventional method. The mechanism of large electric-induced strain is studied in detail through Rietveld refinement, transmission electron microscopy (TEM), and piezoelectric force microscopy (PFM). The BF-BHT-0.05 ceramics, which possess the coexistence of cubic (Pm -3 m) and rhombohedral (R 3 c) phase proved by Rietveld refinement and TEM measurement, have the maximum electric-induced strain of S max = 0.58% at 130 kV/cm (1 Hz). The reduced potential barrier is beneficial to the switching and reorientation of domain under an external electric field due to the coexistence of cubic and rhombohedral phase. A mass of nanodomains embedded into the microdomains, which is conducive to domain switching, are observed obviously through PFM. Therefore, the findings show that the large strain is because the external electric field drives the conversion mixed phase into the major rhombohedral phase, the reduced potential barrier, and the nanodomain in macrodomain. [ABSTRACT FROM AUTHOR]

Highlights: [•] CTNA substituted 50% by La3+ exhibited good microwave dielectric properties. [•] The structure of CTLNA changes from tetragonal to orthorhombic when x ⩾0.5. [•] Intermediate phases disappear when the calcining temperature is higher than 1350°C. [•] 1% SrTiO3 added in CTLNA can reduce the porosity and improve the densification. [ABSTRACT FROM AUTHOR]

Abstract: The effects of LnAlO3 (Ln=La, Nd, Sm) additives on the microstructure and the dielectric properties of Ba4.2Nd9.2Ti18O5 (BNT) materials have been investigated. The microstructure of BNT doped with NdAlO3 was analyzed using X-ray diffraction and scanning electron microscopy (SEM). Over 10wt.% additions of NdAlO3 diminished grain growth and the densifications process. In addition, typical columnar grain morphology observed in BNT ceramics was transformed to quasi-rectangular shapes accompanied by increasing porosity. XRD analysis did not reveal any second phases or modification of the BNT crystal structure. The addition of small amounts of LnAlO3 (≤10wt.%) increased the Q values remarkably and improved the TCf. The relative permittivity and the TCf values showed a linear decrease with increasing additions of LnAlO3. It was observed that near zero TCf values can be achieved with addition of LnAlO3 dopants to BNT ceramics. The Q values exhibited a non-linear behaviour with LnAlO3 additions with maxima attained at approximately 10wt.% LnAlO3. [Copyright &y& Elsevier]

The influence of TiO 2 /Sb 2 O 3 (Ti/Sb) ratio on the microstructure development and electrical properties of varistor ceramics in ZnO–(Bi 2 O 3 –TiO 2 –Sb 2 O 3 )–CoO–MnO 2 system was investigated. Characterization of varistors was performed by XRD, SEM, d.c. degradation behavior, and electrical measurements. It is found that the Ti/Sb ratio greatly influences the microstructure and electrical properties of the ZnO varistor. The specimen with Ti/Sb ratio of 5 has the lowest breakdown field (20V/mm) and improved d.c. degradation behavior. [ABSTRACT FROM AUTHOR]

High-performance lead-free piezoelectric materials with high Curie temperature can be used as substitutes for lead-based piezoelectric components to address serious environmental issues. In our works, 0.7Bi 1.05 Fe+3 (1− x) Fe2+ x O 3−δ – 0.3BaTiO 3 (BF–BT– x Fe2+) ceramics, which demonstrate outstanding large-signal piezoelectric coefficient of d 33 * = 510 p.m./V and electric field-induced bipolar strain of Δs p−p = 0.34% (peak-to-peak) at 50 kV/cm. Meanwhile, optimal remanent polarization of P r = 55.8 μC/cm2, piezoelectric coefficient of d 33 = 178 pC/N, and Curie temperature of T c = 485 °C are achieved at x = 0.07. Of particular interesting the preferred strain is observed in BF–BT– x Fe2+ ceramics with major pseudo-cubic phase. Results showed that prior electric properties are derived from synergistic effect of defect dipoles and phase structure together with non-180° domain switch. The defect dipole builds an internal electric field that favors ferroelectric domain formation and polarization. In addition, the formation of defect breaks the geometry symmetry of cubic structure. [ABSTRACT FROM AUTHOR]

The potential of 3D printing to prepare ceramic RF devices is investigated. (1– x)MgTiO 3 – x CaTiO 3 ceramics (x = 0, 0.1, 0.2, and 0.4) are prepared by 3D printing and subsequent sintering. MgTiO 3 and CaTiO 3 , synthesized by conventional solid-state method, are initially dispersed in ultraviolet-curable resins with appropriate dispersant and photoinitiator. After subjecting the printed samples to debinding and sintering, their density, phase composition, microstructure, and microwave characteristic are measured. Calcined powders of (1– x)MgTiO 3 – x CaTiO 3 ceramics are found to maintain a high solid content (up to 80 wt%) in the resin while maintaining reasonable viscosity values. Moreover, the ultraviolet absorptivity of ceramic is a key factor influencing curing depth. The 3D-printed samples also have the same phase composition, higher density, more uniform particle size, and better microwave performance than dry-pressed samples. Finally, a flat Luneburg lens antenna with MgTiO 3 –CaTiO 3 ceramic is realized using Stereolithography. This work helps to promote research on 3D-printed microwave ceramics and the fabrication of complex RF ceramic devices. [ABSTRACT FROM AUTHOR]

Y 2 O 3 ceramics with good dielectric properties were prepared via co-precipitation reaction and subsequent sintering in a muffle furnace. The effects of Nd doping and sintering temperature on microwave dielectric properties were studied. With the increase in sintering temperature, the density, quality factor ( Q × f ), and dielectric constant ( ε r ) values of pure Y 2 O 3 ceramics increased to the maximum and then gradually decreased. The Y 2 O 3 ceramics sintered at 1500 °C for 4 h showed optimal dielectric properties: ε r =10.76, Q × f =82, 188 GHz, and τ f =−54.4 ppm/°C. With the addition of Nd dopant, the Q × f values, ε r , and τ f of the Nd: Y 2 O 3 ceramics apparently increased, but excessive amount degraded the quality factor. The Y 2 O 3 ceramics with 2 at% Nd 2 O 3 sintered at 1460 °C displayed good microwave dielectric properties: ε r =10.4, Q × f =94, 149 GHz and τ f =−46.2 ppm/°C. [ABSTRACT FROM AUTHOR]

YAG ceramics with good dielectric properties were prepared via a modified pyrolysis method, with yttrium nitrate as the yttrium source and combined aluminium sulphate and aluminium nitrate as aluminium sources, and subsequent sintering in a muffle furnace. The effects of the different aluminium sources on the powder characteristic and the impact of sintering temperature, sintering aids (TEOS) and additive (TiO 2 ) on the dielectric properties of the ceramics were studied. The results show that well-dispersed pure YAG nano-powders can be obtained after calcination at 1000 °C with an aluminium sulphate and aluminium nitrate molar ratio of 1.5:2. The relative density, permittivity ( ε r ) and quality factor ( Q × f ) of the YAG ceramics increase with sintering temperature and TEOS addition. TiO 2 can greatly promote τ f to near-zero but decreases Q × f . The relative density, ε r , Q × f and τ f of the YAG–1 wt% TEOS–1 wt% TiO 2 ceramic obtained at 1520 °C are 97.6%, 9.9, 71, 738 GHz and −30 ppm/°C, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transparent MgAl2O4 ceramics were fabricated by using spark plasma sintering. [•] The effects of annealing temperature were studied by PALS and XPS. [•] The critical annealing temperature is 900°C for the optical properties. [•] The concentration of oxygen vacancies decreased after annealed. [•] A certain annealing temperature is corresponding to the best microwave dielectric properties. [ABSTRACT FROM AUTHOR]

Five novel dielectric ceramics Ba5LnMgNb9O30 (Ln=La, Nd, Sm, Gd and Yb) were synthesized using a conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of the prepared ceramics were investigated. Results show that the ceramics exhibit tetragonal tungsten bronze structure with fully occupied A-sites. Only tungsten bronze structure can be observed in the ceramics of which Ln refers to La, Nd, Sm and Gd, while tungsten bronze structure and YbNbO4 were found in the ceramic of which Ln refers to Yb. All the ceramics exhibit high dielectric constant (ε r=272~429), with the ceramics of which Ln refers to La, Nd, Sm and Yb possessing low dielectric loss with the order of 10−3 at 1MHz. By decreasing the rare-earth ionic radius, the transition temperature increases from −114°C to 45°C and then decreases to −58°C, while the maximum dielectric constant increases to 460 at Ln=Sm and subsequently decreases. The phase transition is a diffuse phase transition (DPT) in the ceramics, while the diffuse exponent γ increases gradually as the ionic radius of rare earth element decreases from that of La3+ to that of Gd3+, and decreases thereafter. The temperature coefficients of dielectric constant of the ceramics with Ln=La, Nd, Sm and Yb are −1229ppm/°C, −1542ppm/°C, −1171ppm/°C and −1067ppm/°C respectively in the range of 20–80°C at 1MHz. [ABSTRACT FROM AUTHOR]

• The optimal dielectric and ferroelectric properties were achieved (tanδ = 2.4 at t = 550 °C, p r = 16.4 µC/cm2). • The formation mechanism of ferroelectric gap was discussed in detail. • The contribution of ferroelectric and nonferroelectric factors to D-E hysteresis loops was systematically discussed. Ferroelectric materials show the hysteresis phenomenon in response to external electric field stimulus owing to the nature of their domains. Hysteresis loops seem like a fingerprint of ferroelectric materials, and some useful pieces of information, such as coercive field, remanent polarization, and spontaneous polarization, can be extracted from hysteresis loops. Interestingly, even bananas can also apparently present an electric displacement–electric field (D-E) hysteresis loop. Therefore, various factors, such as domain switching, electric conductivity, and dielectric permittivity, can affect the ferroelectric properties and the shape of D-E hysteresis loops. In this study, the influence of ferroelectric and nonferroelectric factors on ferroelectric properties was investigated by preparing (1- x)BiFeO 3 - x BaTiO 3 - y mol MnO 2 ceramics. Results showed that all D-E hysteresis loops had a gap. The gap was deduced to be relevant to the domain backswitching and capacitance of ceramics that can store and release charge during polarization. Moreover, the round D-E hysteresis loops were mainly attributed to electric conductivity. The 0.3BiFeO 3 –0.7BaTiO 3 –0.5 mol.% MnO 2 ceramic exhibited outstanding electric properties, such as high Curie temperature (T c = 538 °C) and optimal dielectric and ferroelectric properties (tanδ = 2.4 at T = 550 °C, P r = 16.4 µC/cm2 at 150 kV/cm). Introducing MnO 2 into (1- x)BF- x BT ceramics greatly inhibits the formation of defect and increases the insulation resistivity. The gap in ferroelectric loops results from domain backswitching and dielectric permittivity. Meanwhile, the round D-E loops are mainly attributed to the electric conductivity, dielectric permittivity, and domain switching. [Display omitted] [ABSTRACT FROM AUTHOR]

Zirconium tin titanate ceramics, especially the Zr0.8Sn0.2TiO4 (ZST) ceramics, suitable for use in resonators or filters at microwave frequency, have a high Q value and a low temperature coefficient of resonant frequency. However, the sintering temperature still remained as high as 1350 °C. The methods including glass additions, wet chemical processing, and liquid-phase sintering aids have been used to lower the sintering temperature of ZST ceramics. Using glass additives was found to effectively lower the sintering temperature. Nevertheless, it decreased the microwave dielectric properties of ZST ceramics. The wet chemical processes, especially the coprecipitation route, offered advantages over traditional processing techniques, but often required a complicated procedure that would increase the cost and time in fabricating the ZST ceramics. In contrast, the sintering temperature of ZST ceramics with BaCuO2+CuO,CuO, or V2O5 additions could be effectively reduced without decreasing the microwave dielectric properties due to the liquid phase effects. The microwave dielectric properties of ZST ceramics were sensitive to processing conditions and microstructure features. The dielectric constants were not significantly affected by various additives while the quality factors were strongly dependent on the type and the amount of additives. [Copyright &y& Elsevier]

The microwave dielectric properties of (Pb1-xCax)[(Fe0.5Nb0.5)1-y Zry]O3 system (0.4=x=0.6; y=0.05,0.1) have been investigated at microwave frequencies. X-ray diffraction result shows single-phase specimens with an ordered ABO3-type orthorhombic perovskite structure can be obtained using conventional solid-state reaction method in the compositions of (Pb1-xCax)[(Fe0.5Nb0.5)1-yZry]O3(0.4=x=0.6; y=0.05,0.1). The replacement of Zr4+ for [Fe3+/Nb5+] at the B-site considerably improves the loss quality factor Q and does not remarkably affect the dielectric constant e r and the temperature coefficient of resonant frequency tf whose value of nearly 0 ppm °C−1 can be realized at x=0.55 and y=0.1.The Qf0 value and e r for this composition are measured to be 8658 GHz and 85.3, respectively, using the close cavity resonator method. [Copyright &y& Elsevier]

The (1- x)Bi 1.05 FeO 3 - x BaTiO 3 (x = 0.30, 0.31, 0.32, 0.33) (abbrev. (1− x)BF- x BT) ceramics are successfully prepared via conventional solid-state sintering method. The XRD patterns indicate that the (1- x)BF- x BT ceramics possess pure perovskite structures. In addition, the oval P-E hysteresis loops demonstrate high conductive and dielectric losses in (1-x)BF- x BT ceramics. Ferroelectric properties (P r = 18.6 μC/cm2) and high Curie temperature (T c = 472 °C) are obtained in the ceramics. The conductive mechanism is comprehensively investigated by using impedance spectroscopy and XPS. The change in valence state is also characterized by XPS at room temperature, and the partial reduction in Fe3+ to Fe 2+ and Ti4+ to Ti3+ ions decreased the resistivity and the oval and unsaturated P-E hysteresis loop because of the weakly bound electrons. Results of the impedance spectroscopy and XPS indicate that the bulk is primarily responsible for the electric properties, and the charge carrier is mainly doubly ionized oxygen vacancies at the elevated temperature because of the activation energy E a = 0.69 eV. This work provides an instructive method for the fabrication of high-temperature insulation components. • The conductive mechanism is studied by impedance spectroscopy and XPS analysis. • The charge carrier is mainly doubly ionized oxygen vacancy at the elevated. • The appropriate ferroelectric properties (P r = 18.6 μC/cm2) and upper Curie temperature (T c = 472 °C) were obtained. [ABSTRACT FROM AUTHOR]

High electrical conductivity graphene/epitaxial-3C–SiC (G/epi-3C–SiC) composite films have the potential to the applications such as micro-electro-mechanical systems, distributed Bragg reflectors, solar cells, and photocatalysis in harsh environments. In this study, G/epi-3C–SiC composite films were prepared through laser chemical vapor deposition (LCVD) using hexametyldisilane (HMDS) as a safe single precursor. The electrical conductivity (σ) of the composite films reached 2.23 × 104 S/m, which is 2.2 times of the highest σ reported for G/epi-3C–SiC composite. The deposition rate (R dep) of the composite film with the highest σ is 8.2 times of that of the G/epi-3C–SiC with the highest σ ever reported. σ of the pure epitaxial 3C–SiC film is only 81.2 S/m, which is the lowest value reported to date of 3C–SiC prepared through CVD using HMDS as a single precursor. Elimination of carbon is beneficial for increasing the breakdown field intensity and decreasing the leakage current of heterojunction when epitaxial 3C–SiC is used as semiconductor material. • Graphene/3C–SiC composite films and epitaxial 3C–SiC films were epitaxial grown by LCVD) using HMDS as a single precursor. • The highest electrical conductivity (σ) of the composite films reached 2.23 × 104 S/m. • The σ of the 3C–SiC films decreased to 81.2 S/m, which is the lowest value reported of prepared by CVD using HMDS. [ABSTRACT FROM AUTHOR]