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Single-source-precursor derived ceramics exhibit advantages for the preparation of Si-based ceramics with controllable phase composition and adjustable functional/mechanical properties, which has significant potential for (ultra)high temperature ceramic materials. Within the present work, a series of hafnium/boron-containing Si 3 N 4 -based ceramics (SiHfBCN) are prepared upon pyrolysis/annealing of the corresponding single-source-precursors in N 2 atmosphere at different temperatures ranging from 1000 °C to 1700 °C. The high-temperature (micro)structural evolution with respect to the annealing temperatures and boron concentration was studied using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. The results show that the amorphous SiHfBCN ceramics convert upon crystallization into ceramic nanocomposites consisting of a α-Si 3 N 4 matrix with embedded Si, HfB 2 , and HfB x C y N 1– x – y. The formation and stability of HfB x C y N 1– x – y solid solution were discussed in detail. Finally, the oxidation resistance of the obtained α-Si 3 N 4 /HfB 2 /HfB x C y N 1– x – y ceramic nanocomposites was investigated by thermal gravimetric analysis in air. [ABSTRACT FROM AUTHOR]

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was −35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached −29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties. Therefore, the electrical conductivities of the ceramics increased with increasing temperature as both the migration and hopping conductances increased with increasing temperature. Additionally, the increase in temperature enabled the electrons to leap from the valence band into the conduction band, which also improved the electrical conductivity. [ABSTRACT FROM AUTHOR]

The piezoelectric and electromechanical coupling coefficients in conjunction with their temperature stability are the crucial figure-of-merits of piezoelectric materials, due to these properties determine their response sensitivity and operating temperature range, respectively for practical applications. In this work, Sb, (Bi 0.5 Na 0.5)ZrO 3 , and (Bi 0.5 K 0.5)HfO 3 were used to regulate phase transition of KNN-based ceramics, and resultant large piezoelectric constants d 33 ∼ 430 ± 10 pC/N, unipolar strain S uni ∼ 0.18 % at 40 kV/cm, and a high planar electromechanical coupling factor k p ∼ 55 % were observed in the composition with rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence. Ex-situ electric field XRD measurement and TEM observation indicate the outstanding piezoelectric properties are originated from the electric field-induced phase transition, nanodomains and polar nanoregions, which lower polarization anisotropy and facilitate polarization rotation between different crystallographic symmetries. In addition, the piezoelectric properties of the samples with R-O-T phases coexistence show superior temperature stability and fatigue resistance after 106 bipolar electric cycles. The present study not only helps to understand the structural origin of high piezoresponse, but also lays a foundation for the applications of KNN-based ceramics. [ABSTRACT FROM AUTHOR]

With the rapid development of optoelectronic technology, the realization of multi-functional properties of ferroelectrics has recently become a hot research topic. In the present study, a high electrostrictive effect and excellent photoluminescence properties have been achieved by introducing rare earth Er3+ ions into the high-performance 0.96(K 0.48 Na 0.52)(Nb 0.95 Sb 0.05)O 3 -0.04Bi 0.5 (Na 0.82 K 0.18) 0.5 ZrO 3 (0.96KNNS-0.04BNKZ) ferroelectric ceramic. As a result of the Er3+ doping, the ferroelectric long-range order of 0.96KNNS-0.04BNKZ was disrupted, which led to the formation of polar nanoregions and electrostriction enhancement. The sample that was doped with 0.8 mol% Er3+ ions showed a high electrostrictive strain of ∼0.11 % (at 80 kV/cm), with a large electrostrictive coefficient, Q 33, of 0.033 m4/C2. Q 33 was not sensitive to either a temperature change or field cycling. In addition, the Er3+-modified samples showed a bright up-conversion photoluminescence with a strong green emission, which could be explained by the presence of Er3+ activator ions. Furthermore, an excellent optical temperature performance, with a sensitivity of S = 0.0075 K−1 at 570 K, was achieved for the ceramic that was doped with 0.1 mol% Er3+. This sensitivity was higher than for most rare earth-doped ferroelectric materials. Because of these excellent optical and electrical characteristics, the Er3+-doped 0.96KNNS-0.04BNKZ-based ferroelectrics demonstrated promising prospects for applications in optical-electrically integrated and coupling devices. [ABSTRACT FROM AUTHOR]

High-performance dielectric energy storage ceramics has been brought to the fore by data as a result of the rapid rise in new energy development. The dielectric energy storage materials that can withstand harsh environments while having excellent energy storage performance, large breakdown strength, and maximum polarization is highly demanding. Herein, we fabricated the BiScO 3 (BS) modified 0.88(Ba 0.6 Ca 0.4)TiO 3 -0.12Bi[Mg 2/3 (Nb 0.85 Ta 0.15) 1/3 O 3 ] (BCT-BMNT) ceramics with excellent energy storage performance. The experimental results revealed that the breakdown strength of BCT-BMNT- x BS ceramics can be substantially increased by careful engineering of the grain uniformity induced by the incorporation of the BS. The BCT-BMNT-0.2BS ceramic exhibited a considerably optimal recoverable energy storage density of 5.75 J/cm3 along with a high energy efficiency of 89.63 % at 650 kV/cm. Moreover, this sample showed good stability in the temperature range of 20–160 °C and frequency range of 1–500 Hz and excellent fatigue resistance up to 105 cycles. Regarding the pulsed performance, as-prepared sample exhibited excellent power density of 145.30 MW/cm3 and current density of 937.43 A/cm2. Meanwhile, it showed a fast discharge time (t 0.9) of 50.20 ns under the electric field of 460 kV/cm. This study demonstrates the crucial role that BS doping plays in improving the energy storage capabilities of BT-based lead-free ceramics, which pave the way for the use of BT-based ceramics in the field of energy storage. [ABSTRACT FROM AUTHOR]

The research and development of energy storage materials and devices has now become the current hotspot. In this work, we designed high performance (0.93- x)(Bi 0.5 Na 0.5)TiO 3 -0.07BaTiO 3 - x (Sr 0.7 Bi 0.2)TiO 3 (BNT-0.07BT- x SBT) energy storage ceramics with large recoverable energy storage density and high energy efficiency. Results showed that the introduction of SBT into BNT-0.07BT matrix improved the crystal structure symmetry of the material and induced strong relaxation behavior with broadened dielectric peak. The ferroelectric long-term order of the BNT-0.07BT matrix is destructed via SBT modification, yielding the slender P-E hysteresis loop in samples with higher SBT content. Good energy storage performance with large effective energy storage density W rec of 3.26 J/cm3 and high energy storage efficiency η of 90.3% was obtained in 40 mol%SBT -modified sample, under the electric field of 260 kV/cm. The charge-discharge performance test showed that the sample exhibited a short discharge time (t 0.9 = 143 ns) and a relatively high power density (P D = 40.8 MW/cm3) under an electric field of 160 kV/cm. Moreover, sample showed good thermal stability in the temperature range of 30–180 °C and high frequency stability in the frequency range of 1–1000 Hz. As an attractive material for dielectric capacitor, BNT-0.07BT- x SBT energy storage ceramics have potential applications in pulse power systems. [ABSTRACT FROM AUTHOR]

Dense SiC-(Ti x Zr 1–x)B 2 composite ceramics were prepared via solid-state spark plasma sintering (SPS) by controlling the proportion of ZrB 2 (in the range of 5–25 vol%). Through data fitting, a linear functional relationship was established between x and 2θ for the (Ti x Zr 1–x)B 2 solid solution, which rendered it amenable to characterization analysis. The results show that the 2-D morphology of (Ti x Zr 1–x)B 2 tended to transform from angular to round as the ZrB 2 proportion was increased, which was beneficial in crack deflection and increasing the fracture toughness. Moreover, the growth of SiC grains around the solid solution was inhibited, which improved its mechanical properties. The composite ceramic containing 15 vol% of ZrB 2 had the best mechanical properties, with its Vickers hardness, bending strength and fracture toughness reaching 26.12 GPa, 499 MPa, and 6.45 MPa•m1/2, respectively. [ABSTRACT FROM AUTHOR]

(1- x) (0.935BNT–0.065BaTiO 3)- x SrRECoO 4 (BNBT6.5- x SREC, RE = Pr, Eu, Sm)–based lead-free ferroelectric ceramics with large electrostrain and photoluminescence effect were prepared in our work. Through introducing the SREC dopant into BNBT6.5, the long-range ferroelectric order of ceramics was disrupted, inducing a weak polar state dominated by polar nanoregions before applying an electric field. Due to the reversible transition of PNRs under the electric field, the electrostrain was greatly promoted. When the content of SREC was 0.012, large field-induced large strains of 0.38–0.44% were obtained under an electric field of 70 kV/cm, equivalent to a large signal d 33 * (S max / E max) of 543–586 pm/V. Moreover, relying on the luminescence effect of RE3+ ions in SREC, the modified ceramics exhibited strong photoluminescence with bright red or orange emissions, depending on the type of RE elements. However, the strong emission was strongly quenched in samples with a higher SREC content due to the photoluminescence quenching effect of the heavy metal (Co3+) ions in the SREC dopant. The quenching model can be based on the formation of non-radiative recombination centers induced by Co3+ ions, which affect the energy transition of RE3+ ions from the excited state to the ground state. [ABSTRACT FROM AUTHOR]

The effect of Zr4+ substitution for Ti4+ on the phase evolution and microwave dielectric properties of (Cu 1/3 Nb 2/3) 0.25 Ti 0.75- x Zr x O 2 (0 = x ≤ 0.35) ceramics prepared via conventional solid-state method has been investigated. With the increase of Zr substitution, the ceramics exhibit a gradual phase transition from a tetragonal rutile phase to an orthorhombic srilankite phase, where the synthesis of the srilankite phase at atmospheric pressure and temperature below 1200 °C in this study is reported for the first time. The crystal structure is tetragonal rutile type for the unsubstituted composition, orthorhombic srilankite type for the compositions with x > 0.30, and the compositions in between is a two-phase region with a mixture of rutile and srilankite. The Zr substitution has a great influence on the microstructure of the ceramics. In particular, for compositions where x > 0.1, the grain boundaries are surrounded by elongated powdery particles. The microwave dielectric properties of the ceramics are closely related to the phase transition process, in which Q × f is significantly improved and τ f decreases almost linearly with the increase of the content of srilankite phase. Optimum microwave dielectric properties with a permittivity of 35.1, a Q × f value of 7270 GHz, and a near-zero τ f of 9.0 ppm/°C are obtained in the ceramics with x = 0.3 sintered at 1150 °C for 4 h, which provides a new option for microwave devices requiring medium-permittivity dielectric ceramics. [ABSTRACT FROM AUTHOR]

YCr 0.5 Mn 0.5 O 3 (YCM)-CaCu 3 Ti 4 O 12 (CCTO) ceramics were prepared using a solid processing method, and their properties were studied. XRD measurements showed that all prepared ceramics had pure perovskite structures. With increasing YCM content, grain size in ceramics decreased, and the resistivity of materials was found to be very sensitive to grain size and grain size distribution. Moreover, ceramics had NTC characteristics, and values of ρ 25 , B 25/75 , and E a ranged from 2.21 × 106–7.30 × 106 Ω cm, 5797–6300 K, and 0.5390–0.5800 eV, respectively. The presence of heterovalent ion pairs in samples suggested that conduction mechanism may have been related to electron hopping. Impedance spectroscopy results showed that excessive doping with YCM resulted in greater contribution from grains to overall resistance of the material. Temperature-dependent electrical relaxation behavior was dominated by short-range movement of charge carriers. [ABSTRACT FROM AUTHOR]

Dielectric capacitors show great potential in superior energy storage devices. However, the energy density of these capacitors is still inadequate to meet the requirement of energy storage applications. In this study, the Bi 0.5 Na 0.47 Li 0.03 TiO 3 - x NaNbO 3 (BNLT- x NN) ceramics were prepared via conventional solid-phase reaction. Results showed that NN can efficaciously enhance the breakdown strength (E b) and the relaxation behavior of the BNLT ceramic because of the broken ferroelectric long-range order. When x = 0.3, the maximum E b reached 350 kV/cm, at which the 0.7BNLT-0.3NN ceramic exhibited the high recoverable energy storage density (W rec) of 4.83 J/cm3 and great efficiency (η) of 78.9%. The ceramic demonstrated good temperature stability at 20 °C-160 °C and excellent fatigue resistance. Additionally, the 0.7BNLT-0.3NN ceramic presented high power density (P D ; ∼77.58 MW/cm3), large current density (C D ; ∼861.99 A/cm2), and quite short discharge time (t 0.9 ; ∼0.090 μs). These results indicated that the 0.7BNLT-0.3NN material has excellent energy storage properties and various application prospects. [ABSTRACT FROM AUTHOR]

SiC composite ceramics have good mechanical properties. In this study, the effect of temperature on the microstructure and mechanical properties of SiC–TiB 2 composite ceramics by solid-phase spark plasma sintering (SPS) was investigated. SiC–TiB 2 composite ceramics were prepared by SPS method with graphite powder as sintering additive and kept at 1700 °C, 1750 °C, 1800 °C and 50 MPa for 10min.The experimental results show that the proper TiB 2 addition can obviously increase the mechanical properties of SiC–TiB 2 composite ceramics. Higher sintering temperature results in the aggregation and growth of second-phase TiB 2 grains, which decreases the mechanical properties of SiC–TiB 2 composite ceramics. Good mechanical properties were obtained at 1750 °C, with a density of 97.3%, Vickers hardness of 26.68 GPa, bending strength of 380 MPa and fracture toughness of 5.16 MPa m1/2. [ABSTRACT FROM AUTHOR]