Conventional Solid-state Technique Research Articles

Lithium-modified (K0.5Na0.5)NbO3–BiAlO3 lead-free piezoelectric ceramics with high Curie temperature

Lead-free piezoelectric ceramics based on the perovskite solid solution 0.995(K0.5Na0.5)1−xLixNbO3–0.005BiAlO3 were prepared using conventional solid-state sintering techniques. According to the analysis of X-ray diffraction patterns, a pure perovskite phase structure could be achieved in the studied composition range of 0≤x≤0.08. As the lithium content increased, the crystal structure gradually transitioned from orthorhombic to tetragonal symmetry. Furthermore, an orthorhombic–tetragonal phase boundary could be observed in ceramics with the compositions of 0.03≤x≤0.05. The ceramics with compositions close to the orthorhombic–tetragonal phase boundary exhibited enhanced piezoelectric activity, possessing the largest values of piezoelectric constant d33, and planar and thickness electromechanical coupling coefficients, of 182 pC/N, 0.375, and 0.460, respectively. Additionally, it was found that these ceramics with excellent piezoelectric properties also possessed a high Curie temperature (~ 450°C), indicating that they would be suitable for application in elevated-temperature piezoelectric devices.

Dielectric Properties of SrMnO3-doped K0.5Na0.5NbO3 Lead-Free Ceramics

(1−x)K0.5Na0.5NbO3-xSrMnO3 (0.02 ≤ x ≤ 0.08) (KNN-xSM) ceramics were fabricated by a conventional solid-state technique. X-ray diffraction of the samples revealed that the crystal structure changes from orthorhombic to tetragonal, and finally to pseudocubic symmetry with increasing x. Temperature dependence of dielectric properties showed that the temperature (T m) corresponding to the maximum of dielectric permittivity decreased with increasing x. Two dielectric relaxation processes occurred at high temperatures, which were attributed to grain and grain boundary responses, respectively. Polarization hysteresis loops (P-E) at different electrical fields were displayed. P rmax degenerated with the increase of SM due to the thermally activated leakage current increases. The relationship between electrical properties and defect compensation mechanism is discussed.

Effects of Y2O3/CeO2 co-doping on microwave dielectric properties of Ba(Co0.6Zn38)1/3Nb2/3O3 ceramics

The effects of CeO2/Y2O3 co-doping on the microstructure and microwave dielectric properties of Ba(Co0.6Zn0.38)1/3Nb2/3O3-xA-xB (x = 0,1,2,3,4,6; A = 0.1204 wt%Y2O3; B = 0.1 wt%CeO2) ceramics prepared by the conventional solid-state route technique were investigated. The X-ray diffraction (XRD) results presented that all the well sintered samples exhibited the main phase BaZn0.33Nb0.67O3Ba3CoNb2O9. A certain amount of Ba8CoNb6O24 surface secondary phase and minority phase of Ba5Nb4O15 were also observed in all sintered ceramics. The 1:2 B-site cation ordering degree was found to influenced by the substitution of Y3+ and Ce4+ in the crystal lattice, especially for x = 0.02. Then the scanning electron microscopy (SEM) picture of the optimally well-sintered (1350 °C for 20 h) ceramic has shown a dense microstructure. Although the εr almost kept unchanged, appropriate doping content would greatly improve the Q × f value. Meanwhile, the τf value first declined and then increased with increasing x. At last, the excellent microwave dielectric properties of εr = 36.09, Q × f = 72006 GHz, τf = 3.35 ppm/ºC were obtained for the ceramic with x = 0.02 sintered in air at 1350 °C for 20 h.

An In-Depth Study of Redox-Induced Conformational Changes in Charge Transport Characteristics of a Ferrocene-Alkanethiolate Molecular Electronic Junction: Temperature-Dependent Transition Voltage Spectroscopy Analysis

We studied the temperature-dependent electrical properties of ferrocene-alkanethiolate molecular electronic junctions fabricated by a conventional solid-state device technique using a conducting polymer poly(3,4-ethylenedioxythiophene) stabilized with a poly(4-styrenesulfonic acid) (known as PEDOT:PSS) interlayer. We had previously observed unusual temperature-dependent electrical characteristics at a voltage polarity larger than +0.6 V and at temperatures higher than ∼220 K (see Adv. Funct. Mater. 2014, 24, 2472). The origin of this distinctive behavior was ascribed to redox-induced conformational changes of the ferrocene-alkanethiolate molecules. We performed temperature-dependent transition voltage spectroscopy analysis based on the multibarrier tunneling model to support the proposed redox-induced conformational changes observed in the ferrocene-alkanethiolate molecular junctions. The obtained results were consistent with the unusual thermal characteristics of the ferrocene-alkanethiolate molecular junctions predicted by the proposed redox-induced conformational changes of the molecules.

Sintering behavior, ac conductivity and dielectric relaxation of Li1.3Ti1.7Al0.3(PO4)3 NASICON compound

The phenomenon of relaxation in dielectric materials is described as one of the powerful tools to determine the behavior and properties of ion transport. The kinetics of ionic species and dipole in solid-state electrolyte are dependent on frequency, temperature, and dielectric relaxation. Li1+xTi2−xAlx(PO4)3 conducting solid state electrolyte with x=0.3 was synthesized via conventional solid state technique using the raw materials Li2CO3, TiO2, Al2O3, and NH4H2PO4 as starting materials. TGA/DTG and X-ray diffraction measurements were carried out to study the thermal behavior and phases of the composition. It was observed from the TGA/DTA curves that there is no mass loss above 500°C. The XRD peaks were observed to start appearing at 500°C which corresponds to small peaks in TGA. It was also pointed out that at increasing sintering temperatures from 700°C to 1000°C the number of phases drastically decreased which is attributed to the complete chemical reaction. Temperature and frequency dependence of dielectric relaxation and electric modulus of the compounds were investigated at temperatures 30–230°C and at frequencies of 40kHz–1MHz. The findings showed that the dielectric relaxation peaks shift to higher temperature as frequency increases and the change in ac conductivity with frequency is in agreement with Jonscher’s power law.

Electrical properties, conduction mechanism and modulus of diphosphate compounds

Rubidium aluminium diphosphate was synthesized by a conventional solid-state technique and its conduction properties determined by impedance spectroscopy.

DC conductivity and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in LiFeP2O7 ceramic

A lithium iron diphosphate LiFeP2O7 ceramic was synthesized by the conventional solid state technique. X-ray diffraction analysis indicates the formation of a single-phase monoclinic structure. Electrical properties were studied using complex impedance spectroscopy as a function of frequency (200Hz to 5MHz) at various temperatures (573–708K). As a result, an electrical equivalent circuit has been proposed. The AC conductivity behavior of the compound has been analyzed by Jonscher's universal power law. The scaling behavior in the AC conductivity data has been studied by hopping frequency (ωh) and DC conductivity (σdc). The non-overlapping small polaron tunneling model (NSPT) has been proposed as a closely good model to describe the dominant conduction mechanism.

Nano-to millisecond lifetime luminescence properties in Ln2(WO4)3 (Ln = La, Ho, Tm and Eu) microcrystalline powders with different crystal structures

Ln2(WO4)3 crystals (Ln = La, Ho, Tm, Eu) have been synthesized using the conventional solid-state ceramic technique. X-ray diffraction was employed to identify the crystal structure of the compounds. Depending on the ionic radii of RE3+, two different structures are found, α-Eu2(WO4)3 (modulated scheelite-type) or γ-Sc2(WO4)3 (phase with negative thermal expansion coefficient). The optical characterization is based on absorption, photoluminescence, excitation and kinetic decay studies. Under UV excitation at the (WO4)2− absorption band, two different behaviors are recorded. La2(WO4)3 compounds show a broad visible emission band with a nanosecond range decay rate, and no energy transfer (ET) from the (WO4)2− moiety to the lanthanide ion is observed. However, evidences of ET are observed for Ln = Tm, Ho and Eu. In particular, the (WO4)2− → Eu3+ ET is so high that the fluorescence of the (WO4)2− moiety is almost completely quenched. Consequently, upon UV excitation Eu2(WO4)3 provides an intense visible emission with a 120 μs day lifetime. Although (WO4)2− → Ln3+ ET also occurs for Ln = Ho and Tm, the relatively small energy gap between energy levels of these ions avoids any detectable luminescence, which is quenched by multiphonon processes. Moreover, the effect of a structural phase transition in Ho2(WO4)3 crystals on their luminescence properties is analyzed. The broad range of PL response of Ln2(WO4)3 under UV excitation both in the spectral position of the emission bands (from UV to visible) as well as in the decay range (from ns to hundreds of μs) shows the tunability of wolframates for scintillator applications.

Stability and coloring properties of Ni-qandilite green spinels (Ni,Mg)2TiO4: The “half color wheel” of Ni-doped magnesium titanates

Solid solutions of Ni-doped qandilite spinel (Mg2−xNixTiO4, x = 0–0.4) prepared by solid-state and citrate-gel routes were investigated as potential ceramic pigments or dyes. Fired powders were characterized by conventional solid-state and color-measurement techniques. The increase of Ni-doping favored qandilite decomposition in Ni-geikielite (Ni,Mg)TiO3 and Ni-periclase (Ni,Mg)O. In the ceramic route, Ni-doped qandilite was stabilized at 1400 °C, but still accompanied by small amounts of MgTiO3 and MgO. Remarkably, the citrate-gel route enabled the formation of single-phase qandilite already at 1200 °C (up to 10%mol Ni), and at 1400 °C for all amounts of Ni-doping. Ni-doped qandilite developed green colors due to Ni2+ ions allocated exclusively in octahedral sites of qandilite spinel, being the green colors of higher chroma in citrate-gel powders. Ni-qandilite powders were chemically instable in low-temperature (950–1050 °C) ceramic glazes, acting only as yellow ceramic dyes. Optical properties of Ni-doped karrooite, geikielite and qandilite pigments were compared.

Low Cost, High Energy Density Na-Ion Batteries

Lithium-ion (Li-ion) batteries have been commercially available since the 1990s and currently provide the technology of choice for applications where high energy densities are required. Sodium-ion (Na-ion) technology is similar in many ways to Li-ion technology, but is still in its commercial infancy. Recent interest in Na-ion technology, however, has shown that Na-ion batteries offer several commercial advantages, including lower cost, greater sustainability and improved safety characteristics.1,2 Of the many types of Na-based active materials available, layered oxides such as NaxMO2 (M = transition metal) have recently shown promise in terms of both performance and cost.3,4 These layered oxides can conform to several structural types, the most common of which are O3, P2 and P3, as designated by Delmas et al.5In these descriptions, the O and P refer to an octahedral (O), or prismatic (P), coordination of the Na-ions, and the number refers to the number of layers in the unit cell. The data presented here show the electrochemical performance of a material from the NaaNi(1-x-y-z)MnxMgyTizO2 range, which is covered by a recent Faradion patent application. The material was synthesised via a conventional solid state technique, targeting a stoichiometry to maximise capacity whilst minimising cost and eliminating impurities. In the as-made material, nickel and magnesium are present as M2+, whereas manganese and titanium are present as M4+. The material was electrochemically evaluated in small scale Na-ion pouch cells, using a CC/CV testing regime. Electrodes of ~ 3 mAh/cm2 were used and these were cycled against a commercially available hard carbon, at 30 °C, using an NaPF6-based electrolyte. Figure 1 shows the low rate (~ C/10) voltage profiles of this material vs. hard carbon. A reversible capacity of 132 mAh/g (cathode) is achieved, at an average discharge voltage of 3.44 V, giving a cathode specific energy of 453 Wh/kg, which is comparable to commercially available Li-ion cathode materials. Figure 2 shows the typical life cycle behaviour of this material. The data were collected at a rate of ~ C/10, using voltage limits of 4.3 V and 1.0 V. A reversible capacity of 117 mAh/g (cathode) is retained after 100 cycles, indicating a discharge capacity retention of 97 %. Most of this loss in capacity is recoverable when lower discharge rates are used, suggesting that this is due to cell impedance changes, rather than an irreversible loss of Na. Figures 3 and 4 show the rate capability behaviour of a typical example of this material. This shows good rate capability up to rates of 2C and moderate rate capability at a rate of 4C. This is a notable result, as this material has not yet been optimised for power applications. Subsequent low rate cycling allows higher capacities to be re-accessed, signifying that the loss of capacity is recoverable.

Effects of Y2O3 substitution on microwave dielectric properties of Ba(Co0.6Zn0.38)1/3Nb2/3O3 ceramics

The effects of Y2O3 substitution on the microstructure and microwave dielectric properties of Ba(Co0.6−xYxZn0.38)1/3Nb2/3O3 (x = 0–0.06) ceramics prepared by the conventional solid-state route technique were investigated. The X-ray diffraction results presented that all the well sintered samples exhibited the main phase BaZn0.33Nb0.67O3–Ba3CoNb2O9 and a certain amount of Ba8CoNb6O24 second phase. The 1:2 B-site cation ordering degree was found to influenced by the replacement of Y3+, especially for x = 0.02. Then the scanning electron microscopy pictures of the optimally well-sintered (1375 °C for 20 h) ceramics has shown a dense microstructure. Although the e r almost kept unchanged, appropriate doping content would greatly improve the Q × f value. Meanwhile, the τ f value increased slightly with increasing x. At last, the excellent microwave dielectric properties of e r = 35.21, Q × f = 72,046 GHz, τ f = 3.65 ppm/°C were obtained for x = 0.02 sintered in air at 1375 °C for 20 h.

AC Losses in YBCO-Added Bi1.6Pb0.4Sr2Ca2Cu3O δ Superconductors

The effect of YBCO adding on the superconducting of BPSCCO system with nominal starting composition of (Bi1.6Pb0.4Sr2Ca2Cu3O δ )1−x(YBCO) x with x = 0.00−0.10 was studied. The preparation methods used to prepare the samples are the conventional solid-state techniques. From the XRD data, it is observed that the percentage of the Bi-2223 phase increases and Bi-2212 decreases for addition x = 0.02–0.04, respectively. The effect of YBCO addition on the BPSCCO system also has been investigated in term of AC susceptibility study. We have studied the various applied field dependence of the AC susceptibility in polycrystalline samples. The AC susceptibility measurements in the range 0.05 to 2.00 Oe show that as the applied fields increases, the intergranular AC loss peaks move to lower temperature, and also height decreases and width increases. The effect of YBCO addition for the intergranular critical current J cm, and the presence of weak links that coupled the superconducting grains were defined.

Enhancement of Curie temperature of barium hexaferrite by dense electronic excitations

Curie temperature of polycrystalline barium hexaferrite (BaFe12O19), prepared by conventional solid state technique, is anomalously and significantly enhanced (by nearly 15%) by energetic heavy ion irradiation (150 MeV, Ag12+) at ambient temperature due to dense electronic excitations Moderate fluence (1 × 1012 ions/cm2) induces structural defects giving rise to above enhancement. As established by X-ray diffraction, scanning electron microscopy and Raman studies, higher fluence (1 × 1013 ions/cm2) has structurally transformed the sample to amorphous phase with marginal change in magnetization and Curie temperature.

Role of acentric displacements on the crystal structure and second-harmonic generating properties of RbPbCO3F and CsPbCO3F.

Two lead fluorocarbonates, RbPbCO3F and CsPbCO3F, were synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. RbPbCO3F and CsPbCO3F were structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of corner-shared PbO6F2 polyhedra. For RbPbCO3F, infrared and ultraviolet–visible spectroscopy and thermogravimetric and differential thermal analysis measurements were performed. RbPbCO3F is a new noncentrosymmetric material and crystallizes in the achiral and nonpolar space group P6̅m2 (crystal class 6̅m2). Powder second-harmonic generation (SHG) measurements on RbPbCO3F and CsPbCO3F using 1064 nm radiation revealed an SHG efficiency of approximately 250 and 300 × α-SiO2, respectively. Charge constants d33 of approximately 72 and 94 pm/V were obtained for RbPbCO3F and CsPbCO3F, respectively, through converse piezoelectric measurements. Electronic structure calculations indicate that the nonlinear optical response originates from the distorted PbO6F2 polyhedra, because of the even–odd parity mixing of the O 2p states with the nearly spherically symmetric 6s electrons of Pb2+. The degree of inversion symmetry breaking is quantified using a mode-polarization vector analysis and is correlated with cation size mismatch, from which it is possible to deduce the acentric properties of 3D alkali-metal fluorocarbonates.

High di-electric constant nano-structure ceramics synthesis using novel electric discharge assisted mechanical milling and magneto ball milling and its properties

The conventional method to prepare functional oxides is ceramic-powder-based processing typically via solid-state reaction of microcrystalline starting powders at high temperatures. Disadvantages of this approach include the high temperatures of reaction, limited degree of product chemical homogeneity and difficulties in achieving rapid sintering. Various chemical-based processing routes have been developed to prepare powders of more homogeneous composition, improved reactivity and sintering ability at low temperatures. Regardless of the route chosen to synthesise complex oxides, almost all of them require lengthy heat treatment schedules that usually exceed 10 h, as well as multi-stage processing steps. We describe two approaches to address these problems, applied to successful synthesis of both MgAl 2 O 4 and CaCu 3 Ti 4 O 12 (CCT) oxides exhibiting excellent di-electric properties. One approach employed the novel direct synthesis technique of electric discharge assisted mechanical milling (EDAMM) and the second used the more conventional method of controlled ball milling using the magneto-mechanical method followed by heat treatment of nano-structural products. By using EDAMM, nano-crystalline precursors for transformation into high di-electric constant ceramics could be formed in as little as 0.1% of the processing time required for conventional solid-state techniques while ball milling using the magneto method also resulted in nano-structural precursors powders suitable for reaction by heat treatment to form oxide supercapacitor. Sample characterisation was carried out using XRD, TEM and SEM. Di-electric property measurements were performed using AC-LCR and by DC meters.

Thermoelectric properties of Au-containing type-I clathrates Ba8AuxGa16−3xGe30+2x

Abstract Type I clathrates, with compositions based on Ba 8 Ga 16 Ge 30 , are a class of promising thermoelectric materials due to their intrinsically low thermal conductivity. It has been demonstrated previously that the thermoelectric performance can be improved by transition metal substitution of the framework atoms. In this study, the effects of Au substitution for Ga/Ge on thermal and electrical transport properties of type I clathrate compounds have been investigated. Polycrystalline samples with a large range of Au content have been synthesized using conventional solid state techniques with the actual compositions of resulting materials approximately following Zintl-Klemm rules. The charge carrier type changes from electrons ( n ) to holes ( p ) as the Au content increases. The Seebeck coefficient ( S ) and power factor ( S 2 / ρ where ρ is the electrical resistivity) were improved by Au substitution and the resulting overall thermoelectric properties were enhanced by Au substitution as compared to polycrystalline Ba 8 Ga 16 Ge 30 . The thermoelectric figure of merit ZT attains a value of 0.63 at 740 K for the composition Ba 8 Au 5.47 Ge 39.96 , a value that is somewhat lower than those reported previously. The results presented herein show that Au-containing type I clathrates are promising p- type thermoelectric materials for high temperature applications.

Sulfurization synthesis and photocatalytic activity of oxysulfide La3NbS2O5

The oxysulfide La3NbS2O5 was synthesized by sulfurization using H2S and characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS) and field emission scanning electron microscopy (FE-SEM). The relationship between the sulfurization conditions and the photocatalytic activities for H2 evolution was investigated. Sulfurization method allowed for synthesis of La3NbS2O5 at much lower temperatures and significantly shortened reaction time of 1 h compared with conventional solid-state techniques. The particle morphologies were regular platelike with sizes of 0.1–0.6 μm and smooth surfaces. The highest activity for H2 evolution was obtained at 1073 K for 1 h, which was about 1.83 times that of La3NbS2O5 prepared by solid-state method.

Wet-Chemical Synthesis and Consolidation of Stoichiometric Bismuth Telluride Nanoparticles for Improving the Thermoelectric Figure-of-Merit

Bismuth telluride nanoparticles (NPs) have been synthesized using a low-temperature wet-chemical approach from bismuth(III) oleate and tri-n-octylphosphine telluride. The size and shape of the NPs can be controlled by adjusting the temperature, reaction time, and nature of the surfactants and solvents. Aromatic hydrocarbons (toluene, xylenes) and ethers (phenyl- and benzyl-ether) favor the formation of stoichiometric Bi2Te3 NPs of platelike morphology, whereas the presence of oleylamine and 1-dodecanethiol yields Bi-rich Bi2Te3 spherical NPs. XRD, IR, SEM, TEM, and SAED techniques have been used to characterize the obtained products. We show that the surfactants can be efficiently removed from the surface of the NPs using a two-step process employing nitrosonium tetrafluoroborate and hydrazine hydrate. The surfactant-free NPs were further consolidated into high density pellets using cold-pressing and field-assisted sintering techniques. The sintered surfactant-free Bi2Te3 showed electrical and thermal properties comparable to Bi2Te3 materials processed through conventional solid state techniques, and greatly improved over other nanostructured Bi2Te3 materials synthesized by wet-chemical approaches.

Phase transition and electric properties of (1 − x)BaTiO3–xSr1.9Ca0.1NaNb5O15 perovskite solid solutions

(1 − x)BaTiO3–xSr1.9Ca0.1NaNb5O15 [(1 − x)BT–xSCNN, 0 ≤ x ≤ 0.05] ceramics were prepared by conventional solid-state processing technique. Lorentzian function was used to fit the diffraction lines of the X-ray diffraction patterns, and obtained a structural phase transition from tetragonal to rhombohedral. The structural parameters were refined by the Rietveld method using Maud software from the X-ray diffraction patterns of BT–SCNN ceramics. The lattice parameters were found to decrease with increasing the concentration of SCNN. From the Arrhenius plots, the calculated activation energies of the relaxation and the conduction indicated that both the relaxation processes and conduction were thermally activated, and oxygen vacancies were the possible ionic charge carriers at high temperatures. The polarization study revealed a well-saturated hysteresis loop.

Solid solution studies of layered honeycomb-ordered phases O3–Na3M2SbO6 (M=Cu, Mg, Ni, Zn)

Complete solid solutions with the composition Na3M2−xM′xSbO6 where M, M′=Cu, Mg, Ni, Zn have been synthesized by conventional solid state techniques and were investigated using X-ray diffraction, magnetic susceptibility and optical measurements. All compositions crystallize in a monoclinic unit cell and exhibit a layered structure with a honeycomb cationic ordering within the slabs. These compounds also exhibit Curie–Weiss behavior at high temperature and the magnetic moment values verify the presence of Cu2+ and/or Ni2+. The antiferromagnetic order of Na3Ni2SbO6 is suppressed upon substitution of Ni2+ with Mg2+ or Zn2+. The spin gap observed in Na3Cu2SbO6 is also suppressed by substitution of Cu2+ with Mg2+ or Zn2+. The Na3Ni2−xCuxSbO6 compositions follow an expected transition from an antiferromagnetic ordering to the spin gap of the copper end member. The estimated band gaps for these compounds have been determined from diffuse reflectance measurements.