Reduced Defect Concentration Research Articles

Simultaneously achieved high piezoelectricity and resistivity in CaBi2Nb2O9-based ceramics with high curie temperature

To guarantee the functional operation of high-temperature piezoceramics in harsh circumstances, both large piezoelectricity and superior resistivity are prerequisites. However, it remains a formidable challenge to achieve these objects. Herein, we report Ce-doped CaBi2Nb2O9-based high-temperature polycrystals, which can simultaneously deliver a high piezoelectric coefficient d33 of 21.8 pC/N and decent resistivity ρ of 7.1 × 107 Ω﹒cm at 500 °C, along with a high Curie temperature of 916 °C. More encouragingly, the materials are also gifted with exceptional thermal stability ( < 10% variation of d33 in a broad range from ambient temperature up to 900 °C). In-depth multiscale structural characterizations unveil that the outstanding comprehensive performance of Ce-doped CaBi2Nb2O9-based ceramics originate from the synergistic effects of refined grain size and domain morphology, and reduced defect concentration. This work not only demonstrates that CaBi2Nb2O9-based ceramics hold enormous potential for high-temperature implements, but also offers prospects to exploit high-performance high-temperature piezoceramics.

Double‐ended passivator enables dark‐current‐suppressed colloidal quantum dot photodiodes for CMOS‐integrated infrared imagers

AbstractLead sulfide (PbS) colloidal quantum dot (CQD) photodiodes integrated with silicon‐based readout integrated circuits (ROICs) offer a promising solution for the next‐generation short‐wave infrared (SWIR) imaging technology. Despite their potential, large‐size CQD photodiodes pose a challenge due to high dark currents resulting from surface states on non‐passivated (100) facets and trap states generated by CQD fusion. In this work, we present a novel approach to address this issue by introducing double‐ended ligands that supplementally passivate (100) facets of halide‐capped large‐size CQDs, leading to suppressed bandtail states and reduced defect concentration. Our results demonstrate that the dark current density is highly suppressed by about an order of magnitude to 9.6 nA cm−2 at −10 mV, which is among the lowest reported for PbS CQD photodiodes. Furthermore, the performance of the photodiodes is exemplary, yielding an external quantum efficiency of 50.8% (which corresponds to a responsivity of 0.532 A W−1) and a specific detectivity of 2.5 × 1012 Jones at 1300 nm. By integrating CQD photodiodes with CMOS ROICs, the CQD imager provides high‐resolution (640 × 512) SWIR imaging for infrared penetration and material discrimination.image

Study on Estimation of Device Yield in Non-Epitaxial 4H-SiC Material Relating to Defect Densities Influencing Bipolar Degradation with XRT- Measurements

Commercially available 4H-SiC substrate quality has improved over time, and this has extensively reduced defect concentration in the active epitaxial layer, during epi growth conditions at the interface. The objective of this work is to investigate bulk crystal quality for the purpose of future vertical power device fabrication in exfoliated, non-epitaxial, undoped material layers. Mathematical estimations on the device yield fraction, that is immune to bipolar degradation for the suggested future process were calculated based on XRT measurements to detect BPD and TSD densities on donor substrates. The full wafer BPD density maps of on-axis semi-insulating wafer substrates from two vendors were compared.

(Invited) Addressing Key Process and Material Challenges to Enable 2D Transition Metal Dichalcogenide Channels in Advanced Logic Devices

Two dimensional ultrathin layers are considered promising materials to bring new functionalities in nanotechnologies and candidate to replace 3D materials in existing applications. Among this last category, transition metal dichalcogenides (TMDC) like WS2, MoS2, WSe2 are viewed as interesting alternative channels for ultra-scaled CMOS technologies, as silicon is approaching its physical limits. These semiconductor 2D monolayers could bring a decisive advantage in terms of electrostatic control at very low gate length, while maintaining decent carrier transport properties as compared to 3D materials at same dimension. In addition, TMDC should provide improved off current performance as compared to silicon, an important factor to improve the static power efficiency in multibillion transistor chips. Obviously, replacing the channel material of the main device in microelectronics, from silicon to TMDC, comes with a very long list of scientific and technological challenges to be addressed. In this paper we limit our scope to the growth of TMDC, one of the main pillar in this global effort, and share how we addressed some of the challenges related to the formation of 2D semiconductor channels, to enable the fabrication of functioning devices on lab and 300 mm flows.TMDCs thin films grown with metal oxide CVD on substrates with, in some case, the presence of NaCl salts, are demonstrating the largest grain size and the best electrical performance but these processes are hardly compatible with industrial CVD reactors. In contrast we use chemistries more compatible with manufacturing, with the target of growing TMDC on 300 mm substrates. We report on MoS2 and WS2 formed with chemistries using metal organic precursors such as Mo(CO)6 or W(CO)6 and di-hydrogen sulfide grown in customized epitaxial cross flow 200 and 300 mm reactors [1]. We report basic nucleation and growth studies over a large process domain which show the possibility to control the density of nuclei and the subsequent lateral crystal growth while minimizing secondary nucleation and metal particle defectivity.We study the deposition of MoS2 an WS2 on two basic types of substrates defining fundamentally the integration schemes. On one route, dedicated to device performance demonstration, TMDC monolayers are grown on templated substrates like sapphire following a van der Waals epitaxy mode which enables regular orientation of the crystallites and formation of large and oriented domains after grain ripening with reduced defect concentration. The 2D layer is then transferred onto the final substrate for the device formation. With this technique, average mobilities above 30 cm2/Vs have been achieved regularly on MoS2 backgated devices, and the best devices exhibit currents at transfer curve up to 420 mA/mm [2,3]. On the other flow, recent efforts have aimed at growing WS2 directly on various types of amorphous substrate layer typically deposited on 300mm wafer, acting either as bottom gate dielectric or sacrificial layer. This scheme doesn’t require subsequent transfer step. However, after integration, these materials demonstrate performance still substantially lower than with material grown on sapphire [4,5].As the device dimensions has scaled down over the last 20 years, improving the variability at different scales has emerged as major topic in microelectronics. TMDC channels are no exception to this trend despite intrinsic advantage in terms of thickness control. We will share on specific work done on sapphire surface specification and preparation. We have demonstrated that depositing MoS2 on 1° off-A axis C-plane sapphire substrate reduced the dispersion in mobility as compared to similar materials obtained on C-plane oriented on-axis substrates [6]. We have also worked-out in-situ Cl2 etch process to remove the superficial islands grown on top of the first layer MoS2 crystals as this first layer is being closed. The process enables full lateral etching of the secondary layer crystals selectively to the closed first layer. With this process, we observed substantial improvement in the electrostatic control of MoS2 scaled transistors, including threshold voltage variability and improved subthreshold swing control [7].We continue to work out the TMDC growth process to improve the material quality, impacted by the presence of defects at the grain boundaries or intra-grain, aiming to close the gap with advanced logic requirements.1-Caymax & al., SSDM, D-1-03, 20192-D Lin & al., Symposium on VLSI Technology, 1-2, 20213- Wu & al., IEDM, 7.4.1-7.4.4, 20214- Asselberghs & al., IEDM, 40.2.1- 40.2.4, 20205- Smets & al., IEDM, 34.2.1-34.2.4, 20216- Shi & al., ACS nano 15 (6), 9482-9494, 20217- Shi & al., IEDM, 37.1.1-37.1.4, 2021

Probing the Surface and Bulk Electrical Response of MAPbBr3 Single Crystals

Single crystals (SCs) of halide perovskites are rapidly gaining attention over their polycrystalline thin-film counterparts due to their superior optoelectronic properties. One of the various reasons for their improved properties is the reduced defect concentration as compared with thin films. Since their discovery, many efforts have been devoted to discerning the surface and bulk properties of SCs. However, it is difficult to probe the surface and bulk responses of SCs, and only a few reports distinguishing between these properties have been presented. In this study, we distinguished between the surface and bulk electrical responses of methylammonium lead tribromide (MAPbBr3) SCs using impedance spectroscopy (IS). The electrical response of the MAPbBr3 SC was recorded using different optical excitations for the generation of carriers. The Nyquist plots and capacitance–frequency responses observed under blue and red wavelengths differ significantly from each other and were studied systematically. The results obtained suggest that the photocurrent and capacitive response under blue light are higher than those under red light. Moreover, the change in the low-frequency capacitance is lower in the case of blue light. This is because of the polarization of the interface of metal contacts and the surface of SCs or due to defect-mediated conductivity. As the carriers are collected efficiently from the surface following a rapid process, they do not contribute to the capacitance build-up with temperature. To the best of our knowledge, electrical responses such as the impedance and the capacitive response of SCs using different illumination wavelengths and temperatures have been rarely discussed in the literature.

Advance and prospect of metal-organic frameworks for perovskite photovoltaic devices

Improving the long-term stability is now one of the most critical challenges in perovskite photovoltaic devices. Recently, metal-organic frameworks (MOFs) with appreciable chemical and moisture stabilities are increasingly used in optoelectronics devices. The introduction of MOFs into perovskite solar cells has paved an innovative way to address the stability issue. Consequently, the combination of perovskite photovoltaics with MOFs has drawn significant research interest in the perovskite community not only due to the enhanced stability but also for the improved photovoltaic performance resulting from the reduced defect concentration, increased charge-carrier transport, and effective energy-band alignment. This review focuses on the development of MOF-assisted perovskite photovoltaic devices and systematically summarizes the recent progress in this new type of optoelectronic device upon the combination of MOFs and perovskite photovoltaics. We have critically analyzed various functions of MOFs, including individual interlayer, a modifier of the interlayer, and MOFs/perovskite heterojunction. Furthermore, we provide a roadmap about the potential challenges and prospects of MOF-based perovskite solar cells. • Metal-organic frameworks (MOFs) with appreciable chemical and moisture stabilities are increasingly used in optoelectronics devices. • The combination of perovskite photovoltaics with MOFs has drawn significant research interest in the perovskite community not only due to the enhanced stability but also for the improved photovoltaic performance. • Various functions of MOFs, including individual interlayer, a modifier of the interlayer, and MOFs/perovskite heterojunction, have been critically analyzed.

Energy storage properties of Mn-modified (Na0.2Bi0.2Ca0.2Sr0.2Ba0.2)TiO3 high-entropy relaxor-ferroelectric ceramics

It remains a huge challenge to enhance the energy-storage density (ESD) and efficiency (ESE) of Pb-free dielectrics for ES applications. The perovskite structured high-entropy ceramics are regarded as a promising candidate for pulsed power system devices because of their interesting properties originating from high-entropy effect. Nevertheless, the main drawback of high-entropy ferroelectric materials is their relatively low electric breakdown strength. In this study, MnCO3, as an additive, was designed to improve the insulation resistance of (Na0.2Bi0.2Ca0.2Sr0.2Ba0.2)TiO3-x wt% MnCO3 (NBCSBT-xMn) high-entropy relaxor-ferroelectric ceramics via a conventional solid-state technique. The as-prepared pellets have a well-crystallized pseudo-cubic perovskite structure. Excess Mn content can decrease the grain size and dielectric loss and enhance the relaxation factor, active energy and maximum dielectric constant (εm)-dependent temperature (Tm). The ES performance first increased and then decreased. Consequently, the composite ceramics, with × = 0.5, demonstrated an excellent ESE (η) of 70.2% and a high recoverable ESD (Wrec) of 1.56 J/cm3 at 160 kV/cm because of the increased relaxation factor and reduced defect concentration and the adequate grain size. These properties suggest that novel Mn-doped NBCSBT ceramic is attractive for ES applications.

Thermal Dynamic Self-Healing Supramolecular Dopant Towards Efficient and Stable Flexible Perovskite Solar Cells.

Flexible perovskite solar cells (FPSCs) have attracted great attention due to their advantageous traits such as low cost, portability, light-weight, etc. However, mechanical stability is still the weak point in their practical application. Herein, we prepared efficient FPSCs with remarkable mechanical stability by a dynamic thermal self-healing effect, which can be realized by the usage of a supramolecular adhesive. The supramolecular adhesive, which was obtained by random copolymerization of acrylamide and n-butyl acrylate, is amphiphilic, has a proper glass transition temperature and a high density of hydrogen-bond donors and receptors, providing the possibility of thermal dynamic repair of mechanical damage in FPSCs. The adhesive also greatly improves the leveling property of the precursor solution on the hydrophobic poly[bis(4-phenyl)(2,4,6-trimethylphenyl)]amine (PTAA) surface. PSCs containing this adhesive achieve more than a 20 % power conversion efficiency (PCE) on flexible substrates and a 21.99 % PCE on rigid substrates (certified PCE of 21.27 %), with improved electron mobility and reduced defect concentration.

Thermal Dynamic Self‐Healing Supramolecular Dopant Towards Efficient and Stable Flexible Perovskite Solar Cells

AbstractFlexible perovskite solar cells (FPSCs) have attracted great attention due to their advantageous traits such as low cost, portability, light‐weight, etc. However, mechanical stability is still the weak point in their practical application. Herein, we prepared efficient FPSCs with remarkable mechanical stability by a dynamic thermal self‐healing effect, which can be realized by the usage of a supramolecular adhesive. The supramolecular adhesive, which was obtained by random copolymerization of acrylamide and n‐butyl acrylate, is amphiphilic, has a proper glass transition temperature and a high density of hydrogen‐bond donors and receptors, providing the possibility of thermal dynamic repair of mechanical damage in FPSCs. The adhesive also greatly improves the leveling property of the precursor solution on the hydrophobic poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)]amine (PTAA) surface. PSCs containing this adhesive achieve more than a 20 % power conversion efficiency (PCE) on flexible substrates and a 21.99 % PCE on rigid substrates (certified PCE of 21.27 %), with improved electron mobility and reduced defect concentration.

Dodecylamine assisted perovskite growth for high-performance perovskite solar cells with low defect density

We correlated the concentration of alkylamine in the mixed anti-solvent with the growth process of the perovskite films and the defect passivation effect. The assisted crystal growth process based on “Ostwald ripening” was proposed. Benefiting from the assisted growth effect of dodecylamine on perovskite, the perovskite films have improved crystallinity, optimized interface, reduced defect concentration and suppressed non-radiative recombination of carriers. As a result, a power conversion efficiency of 21.67% was obtained for the devices based on mixed anti-solvent. And owing to the inherent hydrophobicity of the alkyl chains, the devices also have excellent humidity stability. This work provides a facile way to obtain high-quality perovskite films.

Promoting the Methane Oxidation on Pd/CeO2 Catalyst by Increasing the Surface Oxygen Mobility via Defect Engineering

AbstractMethane is a useful chemical resource, but removing it, a powerful greenhouse gas, is important to prevent global warming. In this study, the methane oxidation activity of conventional Pd/CeO2 catalyst was improved by enhancing the oxygen mobility of ceria surface via the simple defect engineering. Raman spectroscopy demonstrates that the defect concentration of ceria surface is reduced after high temperature treatments. Cryogenic hydrogen‐temperature‐programmed‐reduction curves indicate that the surface oxygen of ceria in Pd/CeO2 catalysts with the reduced defect concentration became mobile, resulting in the facile reduction at the lower temperature. X‐ray diffraction, X‐ray photoelectron and X‐ray adsorption spectroscopies show that the improvement in the surface oxygen mobility does not originate from the change in PdOx particle size nor its oxidation state. As a result, the temperature of 50 % conversion of methane shifted by 25 °C to the lower temperature on Pd/CeO2 catalyst with the reduced defect concentration. This work highlights that the catalytic activity can be enhanced by promoting the active participation of the surface oxygen of support.

Effects of double heat treatment of NiO hole transport layer on the performance of QLEDs

Parameters affecting the performance of QLED devices using NiO hole transport layer (HTL) thin film via the sol–gel process route were investigated. In the preparation of the NiO HTL thin film, a double heat treatment scheme, crystallization heat treatment at elevated temperatures followed by vacuum annealing treatment at lower temperatures, was introduced to form a crystalline NiO single phase as well as surface phases with reduced defect concentration. The decoupling of crystallization and vacuum annealing treatment of NiO HTL thin film was effective in enhancing the performance of the QLEDs. Also, the insertion of an interlayer between QD EML and NiO HTL was very effective in enhancing the performance of the device. With the modification of processing conditions, the luminance of QLED with the NiO HTL was improved from 30 to 11500 cd/m2 and the current efficiency from 0.25 to 23 cd/A, respectively.

Structural analysis of the fracture surface of a heterogeneous body (quartz sandstone)

The structure of surface layers of quartz sandstone with a thickness of ~1 μm before and after destruction by a compressive stress is studied by methods of infrared, photoluminescent, and Raman spectroscopy. Before destruction, this layer contained quartz grains cemented with montmorrillonite and kaolinite. The grains are covered with a thin water layer and have crystallographic defects: Si–O–, self-trapped excitons, AlOH and LiOH compounds, [AlO4]– centers, etc. The destructed surface contains separate quartz grains with sizes of ~2 μm and a reduced defect concentration. It is assumed that the defects reduce the strength of quartz grains, which are destroyed in the first turn.

High-pressure, high-temperature plastic deformation of sintered diamonds

The strength of polycrystalline diamond (PCD) was investigated through a high pressure (P) and temperature (T) deformation experiment. Prior to the deformation experiment, two bulk samples were sintered back to back under identical conditions with two different precursors, which shared identical initial grain size distribution. Precursor of one sample (2E) had lower concentration of crystalline defects than that of the other sample (1S). In crushing strength tests, precursor of 2E exhibited an enhanced crushing strength compared to that of 1S. During the high P–T deformation experiment, the two samples were stacked back to back and deformed together. Their mechanical properties were investigated in situ using synchrotron X-ray diffraction and imaging in the deformation DIA apparatus. The strain data based on imaging showed that the two samples were deformed at identical strain rates (ca. 1.5×10−5s−1) and analysis based on lattice plane distortions in the diffraction patterns showed that sample 2E exhibits marginally higher strength than that of sample 1S. The X-ray data indicate that, upon deformation, larger elastic lattice strain builds up within the grains in sample 2E, indicating greater strength at grain-to-grain level in this sample. In addition, lower micro-stress levels are evidenced upon hydrostatic loading of sample 2E, strongly indicating a better sintering state than that in sample 1S. We interpret these differences as due to a lower defect concentration, particularly on the grain surfaces of the precursor powder, that results in stronger diamond–diamond bonding. Altogether, these data suggest that the use of diamond grains with reduced defect concentration and cleaner surfaces as precursors will likely improve the wear resistance of the resulting PCD via stronger individual grains and better sintering.

Nongeminate radiative recombination of free charges in cation-exchanged PbS quantum dot films

Using photoluminescence (PL) spectroscopy we explore the radiative recombination pathways in PbS quantum dots (QDs) synthesized by two methods. We compare conventionally synthesized PbS from a PbO precursor to PbS synthesized using cation-exchange from CdS QDs. We show that strongly coupled films of PbS QDs from the cation-exchange luminesce with significant efficiency at room temperature. This is in stark contrast to conventional PbS QDs, which have exceedingly weak room temperature emission. Moreover, the power dependence of the emission is quadratic, indicating bimolecular radiative recombination that is reasonably competitive with trap-assisted recombination, a feature previously unreported in coupled PbS QD films. We interpret these results in terms of a greatly reduced defect concentration for cation-exchanged QDs that mitigates the influence of trap-assisted recombination. Cation-exchanged QDs have recently been employed in highly efficient and air-stable lead chalcogenide QD devices, and the reduced number of trap states inferred here may lead to improved current collection and higher open circuit voltage.

Radiation Stability of Spark‐Plasma‐Sintered Lead Vanadate Iodoapatite

Spark‐plasma‐sintered lead vanadate iodoapatite Pb9.85(VO4)6I1.7, a promising nuclear waste form for the immobilization of I‐129, was irradiated with energetic ions, electrons, and gamma rays, to investigate its radiation stability. In situ TEM observation of the 1 MeV Kr2+ irradiation shows that lead vanadate iodoapatite generally exhibits higher tolerance against ion irradiation‐induced amorphization than lead vanadate fluorapatite, and the spark plasma sintering can further enhance its radiation stability attributed to the enhanced crystallinity, reduced defect concentration, and denser microstructure. The critical amorphization dose and critical temperature for the SPS‐densified iodoapatite at 700°C are determined to be 0.25 dpa at room temperature and 230°C, respectively. No significant phase transformation or microstructural damage occurred under energetic electron and gamma irradiations. Raman spectra of gamma‐ray‐irradiated iodoapatite indicate improved V–O bond order at 500 kGy dose. Generally, the spark‐plasma‐sintered iodoapatite exhibits excellent radiation stability for nuclear waste form applications. The significantly enhanced radiation stability of the SPS‐densified iodoapatite suggests that SPS holds great promise for fabricating iodoapatite waste form with minimum iodine loss and optimized radiation tolerance for effective management of highly volatile I‐129.

Silicon Oxycarbide Ceramics As Anode Materials for Li-Ion Batteries: Modification of the Structure and Composition to Enhance the Li Storage Properties

Li-ion battery technology is one of the promising energy storage solution for the future. Studies based on electrode materials are one of the key step to improve the energy storage performance of these systems. Recent studies shows that polymer derived silicon oxycarbide (SiOC) ceramics can be considered as a potential anode material. SiOC ceramics are generally amorphous in nature and usually consists of a network of disordered free carbon segregated in amorphous SiOC matrix. The complex nanostructure plays a crucial role in determining their functional properties. Carbon rich SiOCs (>20wt% free carbon) is found to be the best candidate for Li storage. The enhanced Li ion storage capacity of SiOC ceramics is generally explained in connection with the disordered free carbon phase which stores lithium in interlayer spaces along with at the edges of the carbon clusters and mixed SiOC phase stoichiometry supporting the stability of the system. The main disadvantage of this material is the first cycle irreversible capacity loss which arises mainly due to the presence of oxygen, defects, micro pores etc. By synthesizing SiOC compositions with different stoichiometry it has been shown that carbon-rich SiOC ceramics with ~50wt% of free carbon and remaining amorphous SiOC matrix is the best candidate for reversible lithium storage demonstrating higher reversible capacity of 600 mAh g-1with a good cycling stability. Within our work SiOC ceramics have been synthesized from polysiloxanes using different cross-linking and heat treatment approach. In a typical preparation a linear polysiloxane is cross-linked with divinylbenzene (DVB) via hydrosilylation reaction in presence of a Pt catalyst. The phenyl groups present in divinylbenzene act as the major carbon source in the final ceramics. Correlating the mixed SiOC stoichiometry composition with initial charging capacity points out a linear trend in capacity increase with amount of mixed bond networks. Mixed SiOC compositions has been characterized using 29Si MASNMR studies. It has been shown that the composition changes with pyrolysis temperature. With increase in pyrolysis temperature there is a phase separation in to SiO4 and SiC4 phases with the consumption of mixed SixOyCz units. Electrochemical studies reveal that 1000 °C is the optimal temperature of pyrolysis to have maximum SiOC capacity with good cycling stability. A specific capacity of ~600 mAh g-1 is recorded at a rate of C/20 (18 mA g-1) with 60 % efficiency. Pyrolysis atmosphere also plays a role in determining the final properties. Using a hydrogen containing atmosphere (Ar/H2 with 5% H2) for pyrolysis helps to increase the specific capacity up to an extent by removing carbon dangling bonds which acts as a trap for irreversible Li storage. This has been well supported by EPR investigations showing reduced defect concentration for H2 pyrolysed samples. A capacity increase of around 150 mAh g-1 is observed for the H2 pyrolysed samples. Recently our research focus turned to porous SiOC ceramic as a perspective anode for high rate Li storage applications. The porous nature of the anode material can enhance the fast charging/discharging behavior by reducing the diffusion path of Li ions due to electrolyte penetration and also the porous space can accommodate the volume changes associated with large Li intake. Aerogel approach is followed to produce SiOC ceramics with controlled porosity. The crosslinking is carried out under highly diluted conditions using acetone as solvent (80 vol% dilution). Wet gels after cross-linking are then aged in respective solvent followed by drying under supercritical conditions using liquid carbon dioxide followed by pyrolysis at 1000 °C under controlled argon atmosphere. Final SiOC ceramic aerogels have ~ 40 wt % of free carbon distributed within remaining SiOC matrix. The BET surface area for aerogel sample equals 180 m2/g. Electrochemical characterization of aerogels reveals a high specific capacity of more than 600 mAh g-1 at a charging rate of C (360 mA g-1) along with a good cycling stability compared to ~300 mAh g-1 recorded for dense SiOC at the same rate and ~400 mAh g-1 for H2 pyrolysed counterparts. Electrochemical studies with different SiOC compositions reveal the excellent Li host properties of these materials. Capacities are enhanced by tailoring the structure and composition of final ceramic. Incorporating Li active hetero elements such as metallic Si, Sn etc. in aerogels may further improve the Li storage performance, i.e. porous matrix can be used to compensate the volume expansion associated with the alloying systems. Figure 1

Enhanced high-field strain and reduced high-temperature dielectric loss in 0.6(Bi0.9La0.1)(Fe1−xTix)O3–0.4PbTiO3 piezoelectric ceramics

0.6(Bi0.9La0.1)(Fe1−xTix)O3–0.4PbTiO3 (BLFT–PT) (x=0, 0.01, 0.02, and 0.04) ceramics were prepared by traditional solid state reaction method. XRD results indicate that BLFT–PT ceramics show the coexistence of rhombohedral and tetragonal phases, and the c/a ratio as well as the fraction of rhombohedral phase decrease with increasing Ti content. Values of the dielectric constant εr, dielectric loss tanθ at 1kHz, Curie temperature Tc, and piezoelectric constant d33 for BLFT–PT ceramics with the composition of x=0.02 were of 682, 0.032, 450°C, and 117C/N, respectively. It is interesting that the maximum strain of BLFT–PT ceramics achieves about 0.2% under the electric field of 120kV/cm, which is twice of that for BLF–PT ceramics without Ti modification and comparable with that of BiScO3–PbTiO3 ceramics. The high temperature dielectric loss was reduced significantly by Ti doping, which was only one tenth of BLF–PT ceramics in the temperature range of 200–400°C. Impedance spectroscopy analysis reflectsthat Ti doping may enhanc the grain resistivity by reduced defect concentration, and thus cause the resistivity of BLFT–PT to increase obviously at elevevated temperatures. These results indicate that BLFT–PT ceramics would be promising candidates for high temperature piezoelectric applications.

Impedance spectroscopy studies of 0.7Bi(Fe1−xGax)O3–0.3PbTiO3 high temperature piezoelectric ceramics

Abstract Crystalline solutions of 0.7Bi(Fe 1− x Ga x )O 3 –0.3PbTiO 3 (BGF–PT) of x = 0, 0.05 and 0.1 were fabricated by solid-state reaction method. X-ray diffraction results indicated that BGF–PT ceramics showed single perovskite structure, and Ga was incorporated into the BGF–PT system. Impedance spectroscopy studies revealed that there were two types of relaxation processes indicating two electro active regions (grain and grain boundary) in BGF–PT of x = 0 over the frequency and temperature range studied, whereas there was only one (grain) for BGF–PT of x = 0.05 and 0.1. Further investigation reflected that the high temperature resistivity of BGF–PT had been improved significantly by Ga modification, which was probably owing to enhanced grain resistivity by reduced defect concentration in the solid solutions.

Facile synthesis of composite g-C3N4/WO3: a nontoxic photocatalyst with excellent catalytic activity under visible light

A novel nontoxic g-C3N4/WO3 composite photocatalyst with an increased surface area but a reduced defect concentration was synthesized, which shows an excellent catalytic performance under visible light irradiation.