Higher Pre-exponential Factor Research Articles

Optimization and kinetic studies for biodiesel production from dairy waste scum oil via microwave assisted transesterification

This study presents an investigation of the optimization and kinetic aspects of the microwave (MW) heating transesterification process for converting dairy waste scum oil (DWSO) into biodiesel using lithium impregnated calcium oxide from eggshell (Li-ECaO) as a catalyst. The transesterification was done via microwave heating while varying catalyst loading (1 – 5 wt%), methanol to oil molar ratio (6 – 18:1), temperature (55 – 75⁰C), and reaction time in the range of 5 – 25 min. Response Surface Methodology (RSM) optimized the process parameters, yielding an impressive 90.5% biodiesel yield. The optimal operating conditions were determined 3 wt% catalyst loading, 18:1 methanol to oil molar ratio, a reaction temperature of 65ºC, and a reaction time of 25 minutes. A thorough kinetic analysis of the transesterification reaction for the MW heating transesterification of DWSO by Li-ECaO was performed at various temperatures (45 – 75ºC). The pseudo-first order kinetic study of the reaction revealed a moderately low activation energy of 38.86 kJ/mol and a high pre-exponential factor of 1141.27 s−1, which is consistent with previous studies. Importantly, the observed activation energy was lower than that of conventional methods, highlighting the potential of MW heating as a viable technique for future biodiesel production, and using wastes such as DWSO and eggshell could contribute to being greener and environmentally friendly.

Improving biomass fuel obtained from Brazil nut residues via torrefaction: A case of kinetic and thermodynamic study

The residues of Brazil nuts (Bertholletia excelsa) were evaluated, in their natural state and in torrefied form, for their energy potential after pyrolysis. Samples of shells (BNS) and husks (BNH) were torrefied at 220, 260 and 300 ºC for 30 and 60 min, and were characterized for their chemical and energetic composition. It was also determined which samples showed, simultaneously, the lowest hemicellulose content and the highest cellulose content after torrefaction via analysis of the decomposition profile at 10 ºC/min under pyrolysis. The evolution of gases such as H2O, CO2 and/or C3H8, and CH4 was observed by simulated pyrolysis on a microscale in a thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS). In addition, the kinetics of the pyrolysis of untorrefied and torrefied samples were evaluated using the Flynn-Wall-Ozawa (FWO) and Vyazovkin (VYZ) models in order to obtain the activation energy, pre-exponential factor and thermodynamic parameters. The predominant reaction mechanism was determined by Criado Master-plot method. The mean value of the activation energies ranged from 132.24 to 134.95 kJ/mol for BNS, from 135.53 to 138.47 kJ/mol for ST263, from 149.10 to 150.96 kJ/mol for BNH and from 145.83 to 148.14 kJ/mol for HT263. It was found that D2 and D4 diffusion mechanisms are prevalent in the decomposition of untorrefied samples, while torrefied samples were better adjusted to the F1/A2/A3/A4 overlapping nucleation models. High pre-exponential factor values indicated the presence of multiple intermolecular collisional reactions. The thermodynamic parameters evaluated, as well as the variations in enthalpy, Gibbs free energy and entropy, indicated that the evaluated process is endothermic, though requires little energy. As a whole, in view of the optimized parameters and elevation of the thermal stability of the material, the results demonstrate good potential for the use of Brazil nut shells and husks torrefied at 260 ºC for 30 min as biochar. In addition, pyrolyzed Brazil nut residues also have great potential in the production of bio-oil and biogas, in view of the high content of volatile matter released during the decomposition of the hemicellulose and lignin.

Effect of demineralization on pyrolysis semi-coke physical and chemical characteristics and oxy-fuel combustion characteristics

With global green and low-carbon development, carbon emission reduction is imminent. Oxy-fuel combustion technology is considered to be one of the most promising carbon capture and carbon sequestration technologies. In this work, the physical and chemical characteristics and oxy-fuel combustion characteristics of semi-coke (SC) and demineralized semi-coke (De-SC) were studied. The result shows that, compared with 20% O2/80% CO2, under 30% O2/70% CO2 atmosphere, the ignition temperature and burnout temperature of De-SC are lower, the maximum combustion rate is higher, and the main combustion process can be clearly divided into homogeneous and heterogeneous combustion stages. Compared with SC, De-SC has a less developed pore structure and lower alkali metal and volatile content, which lead to higher ignition temperatures for De-SC. The demineralization process makes the microcrystalline structure of carbon looser and increases the relative content of oxygen-containing functional groups, which are all beneficial to increasing the reactivity of De-SC. The combustion method of De-SC is mainly the particle surface reaction. Only in the atmosphere of 30% O2/70% CO2 and the heating rate of 30 °C/min the combustion mode of De-SC is on the surface and inside the particles. Under different atmospheres, compared with SC, De-SC has lower activation energy and higher pre-exponential factor. The activation and pre-exponential of De-SC have a kinetic compensation effect. The results of this paper provide a theoretical basis for an in-depth understanding of the application of De-SC under oxy-fuel conditions.

Thermal stability of energetic 6,8-dinitrotriazolo[1,5-a]pyridines: Interplay of thermal analysis and quantitative quantum chemical calculations

Understanding the thermal stability of energetic materials is of great importance for storage and safety issues. In the present work, we report on the thermolysis kinetics and mechanism of the two fused energetic heterocycles, viz., 6,8-dinitrotriazolo[1,5-a]pyridine (1) and 2-amino-6,8-dinitro[1,2,4]triazolo[1,5-a]pyridine (2). The experimental kinetics obtained with the aid of advanced thermal analysis techniques was complemented by mechanistic insights from high-level quantum chemical calculations. More specifically, the simultaneous thermal analysis (STA) revealed that both compounds evaporate under atmospheric pressure. To shift the evaporation to higher temperatures and to study the sole decomposition kinetics, we employed the differential scanning calorimetry (DSC) under elevated external pressure (2.0 MPa). The analysis of DSC data was performed using the Kissinger, isoconversional, and model-fitting approaches. The thermolysis of 1 occurs in the melt and is described by the kinetic scheme comprised of two independent non-integer order autocatalytic reactions with the kinetic parameters Ea1=124.2±0.5 kJ mol−1, log(A1/s−1)=9.34±0.04 and Ea2=80.8±0.7 kJ mol−1, log(A1/s−1)= 4.86±0.07. At the same time, the obtained kinetic parameters for 2 are too large to be realistic, which is a consequence of the overlap of melting and decomposition processes near the melting point. To get a deeper insight into the decomposition mechanism, the experimental data were complemented by theoretical thermolysis pathways with the activation barriers calculated using the domain-based local pair natural orbital (DLPNO) modifications of coupled cluster techniques. The same primary decomposition channels, viz., the nitro-nitrite isomerization and CNO2 bond cleavage turned out to compete in the thermolysis of 1 and 2. Due to a lower activation barrier (∼240 kJ mol−1), the former reaction path dominates at lower temperatures, whereas in the experimental temperature ranges (>500 K) the CNO2 bond cleavage with a higher preexponential factor is the fastest elementary reaction (the activation barrier ∼280 kJ mol−1). The obtained experimental and theoretical Arrhenius parameters exhibit a kinetic compensation effect, that is, the rate constant values in solid, melt, and gas phases are close to each other.

Aliovalent Calcium Doping of Yttrium Oxyhydride Thin Films and Implications for Photochromism.

To develop an understanding of the photochromic effect in rare-earth metal oxyhydride thin films (REH3–2xOx, here RE = Y), we explore the aliovalent doping of the RE cation. We prepared Ca-doped yttrium oxyhydride thin films ((CazY1–z)HxOy) by reactive magnetron cosputtering with Ca doping concentrations between 0 and 36 at. %. All of the films are semiconductors with a constant optical band gap for Ca content below 15%, while the band gap expands for compositions above 15%. Ca doping affects the photochromic properties, resulting in (1) a lower photochromic contrast, likely due to a lower H– concentration, and (2) a faster bleaching speed, caused by a higher pre-exponential factor. Overall, these results point to the importance of the H– concentration for the formation of a “darkened” phase and the local rearrangement of these H– for the kinetics of the process.

Influence of preparation methods in the structure and properties of Fe2O3/g-C3N4 composite catalysts

The control of performance-oriented materials structure will be limited by the preparation of materials, and the research on the correlation between the preparation methods and the target structure will be an interesting direction. In this paper, three kinds of precursor mixture of Fe2O3 and g-C3N4 (FeCl3/DCDA-1, 2, 3) were prepared by mechanical compounding and simple hydrothermal method respectively. After calcination under the same conditions, Fe2O3/g-C3N4 composite catalysts were prepared. The relationship between the structure of the precursor obtained by different preparation methods and the performance of the composite catalyst was studied by thermal decomposition kinetics. The results show that in the simple hydrothermal method, compared with FeCl3/DCDA-3 obtained by drying only the composite crystals precipitated in the mixed solution, the activation energy of FeCl3/DCDA-2 obtained by drying the mixed solution increases with the increase of conversion rate, and has a higher pre exponential factor A value. This may be due to the increasingly strong interaction between Fe(OH)3 and dicyandiamide in FeCl3/DCDA-2, which makes dicyandiamide difficult to be converted into melamine in the calcination process. As a result, the interface interaction between Fe2O3 and g-C3N4 in the composite catalyst becomes stronger, forming a strong Fe–N coordination bond and promoting the separation of electron holes. Fe2O3/g–C3N4–2 has the highest photocatalytic activity among the prepared photocatalysts. It can degrade 62.0% of methylene blue (MB) under visible light irradiation for 60 min, which is 2.32 times that of pure g-C3N4 (34.6%). In addition, under the same conditions, Fe2O3/g–C3N4–2 can degrade 7.72% of ciprofloxacin (CIP).

Characterization and Crystal Nucleation Kinetics of a New Metastable Polymorph of Piracetam in Alcoholic Solvents.

A new polymorph of the drug active pharmaceutical ingredient piracetam (Form VI) has been discovered and characterized by X-ray powder diffraction (PXRD), solid-state Raman, attenuated total reflectance infrared spectroscopy, and differential scanning calorimetry. The PXRD diffractogram of Form VI shows a distinct peak at 24.2° (2θ) that distinguishes it from the previously known polymorphs and solvates. Form VI is metastable with respect to the previously known polymorphs Form II and Form III; in ethanol solution at 288 K, Form VI transforms into Form II within 15 min, while in isopropanol solution Form VI is kinetically stable for at least 6 h. A total of 1200 crystal nucleation induction time experiments of piracetam in ethanol and isopropanol solutions have been conducted, in sets of 40–80 repeat experiments carried out at different temperatures and solute concentrations. Each solution nucleated as a single polymorph, and each set of repeat experiments resulted in different proportions of Form II, Form III, and Form VI, with Form VI dominating at low nucleation temperatures and Form II at higher nucleation temperatures. The induction time data for Form VI at 288 K have been evaluated within the framework of the classical nucleation theory. At equal driving force, nucleation of Form VI is less obstructed in ethanol than in isopropanol, as captured by a lower interfacial energy and higher pre-exponential factor in ethanol. The proportion of Form VI obtained at a comparable driving force increases in the order ethanol < isopropanol.

Ordering processes and atomic defects in FeCo

Abstract The present knowledge on self-diffusion and lattice vacancies in near-stoichiometric body-centred cubic FeCo alloys is critically reviewed and related to the establishment of structural order in the alloy after quenching from elevated temperatures. The available data may be consistently explained in terms of the so-called six-jump cycle mechanism of Huntington, Elcock and McCormick, plus the additional concept of ‘pseudo-selfdiffusivity’. It is shown that this leads to an understanding of the observed combinations of high activation enthalpy and large pre-exponential factor in the Fe self-diffusivity on the one hand, and of a lower activation enthalpy and ‘normal’ pre-exponential factor in the Co self-diffusion on the other hand. For some vacancy properties numerical estimates are given. The potential of muon spin rotation measurements for filling existing gaps in our knowledge is emphasized. A critical discussion of the “500 °C anomaly” shows that the explanations attempted in the literature are unsatisfactory. It is proposed that the tetragonality of the compounds FeCo3 and Fe3Co predicted by ab-initio calculations of Díaz-Ortiz et al. may lead to a metastable pattern of antiphase domains on a very small scale, the dissolution of which may cause the anomaly.

Kinetic investigation of the thermal decomposition of both 3-nitro-2,4-dihydro-3H-1,2,4-triazol-5-one (NTO), and nNTO in the presence of nickel zinc copper ferrite

The catalytic impact of nickel-zinc-copper ferrite (NiZnCuF) on the thermal decomposition of micron and naosize NTO was investigated in this work. NiZnCuF was produced utilising a wet chemical technique with metal nitrate salts as a precursor. Raman, UV–vis, Powder-X-ray diffraction patterns, and Fourier-Transform Infrared Spectroscopy (FT-IR) was employed to characterise NiZnCuF. The synthesized NiZnCuF was incorporated in NTO, and nanosize NTO (nNTO) as a 5 % by mass additive. TG-DSC analysis was used to examine the thermal decomposition of NTO and nNTO samples with and without NiZnCuF. To investigate the catalytic activity of NiZnCuF, kinetic parameters were computed using isoonversional techniques. The results indicated that NiZnCuF can successfully lower the high activation energy and pre-exponential factor of NTO and nNTO (27–34 %), implying a quicker decomposition of NTO and nNTO in the presence of NiZnCuF. The present work provides significant improvement in the thermal decomposition behaviour of NTO using a simple catalyst as an additive. NTO + NiZnCuF composition can be better substitute to NTO in the high energetic explosive formulations for the better thermal performance.

Effect of Curing Agents on Electrical Properties of Low-Temperature Curing Conductive Coatings and Thermodynamic Analysis

Silver-based high-conductivity coatings are used in many advanced manufacturing equipment and components, and existing coatings require high-temperature curing. This paper studies the effects of different curing agents on the electrical properties of low-temperature curing (&lt;100 °C) conductive coatings, and analyzes the effects of different curing temperatures and curing time on the surface resistance, square resistance and resistivity of conductive coatings. The response surface method in Design Expert was used to construct the model, and the curing thermodynamics of different curing agents were analyzed by DSC. It was found that curing agents with lower Tm and activation energy, higher pre-exponential factor and more flexible segments are beneficial to the preparation of highly conductive coatings.

Energy recovery from sewage sludge: Product characteristics, heating value prediction and reaction kinetics

Energy recovery from sewage sludge was carried out by using microwave and conventional torrefaction. The microwave torrefaction was carried out by using a laboratory-scale microwave oven that provides single-mode microwave irradiation at 2.45 GHz, and the amount of sewage sludge for each experiment was approximately 20 g. The efficiency of microwave heating can be substantially promoted at higher power level, resulting in higher heating rate and maximum temperature. According to higher energy yield and heating value of torrefied sewage sludge, the optimum power level for bioenergy produced by microwave torrefaction of sewage sludge should be 200 W. Because of lower mass yield and temperature required to obtain the same yield, microwave heating can be more effective than conventional heating for sewage sludge torrefaction. The elemental composition of torrefied sewage sludge at 400 W was similar to that of anthracite, and its low hydrogen and oxygen contents could prevent excessive formation of smoke. Two correlations were obtained to predict the HHV of SS based on proximate and elemental compositions. With the recovery of liquid and gas products as bioenergy, the energy return on investment for microwave torrefaction of sewage sludge can be up to 16.4, much higher than the minimum value required for a sustainable society. Because of lower activation energy but higher pre-exponential factor, microwave heating can be approximately five times faster than conventional heating.

Effects of cellulose, hemicellulose and lignin on biomass pyrolysis kinetics

In order to investigate interactions among biomass components on pyrolysis kinetics, pyrolysis experiments of individual components, synthetic biomass (designed by Design-Export software) and natural biomass (rice husk and corn straw) were conducted on a thermogravimetric analyzer (TGA). The results revealed that the pyrolysis behavior of cellulose is sharp, which is with low pyrolysis reaction order (1.38), high activation energy (168.61 kJ/mol) and high pre-exponential factor (3.50E+12/s). The pyrolysis behavior of hemicellulose and lignin is slower but more complicated, both with high pyrolysis reaction order (2.30, 1.51), low activation energy (126.31, 87.21 kJ/mol), and low pre-exponential factor (9.67E+09, 2.59E+05 /s). Comparison of the experimental and calculated kinetics of synthetic samples confirmed that interactive effects on pyrolysis kinetics exist in the co-pyrolysis process. In particular, the presence of lignin inhibited the pyrolysis reaction rate of synthetic biomass, and cellulose played the dominant role in the activation energy and frequency factor. The pyrolysis reaction order was strongly influenced by hemicellulose owing to its abundant and complex branched chains. The predicted model was also established for calculating kinetic parameters of natural biomass with known proportions of three components. The predicted results were consistent with the experimental ones, validating the effectiveness of the prediction model.

Kinetic Modeling of Citrullus Lanatus (Watermelon) Peel Using Thermo Gravimetric Analysis

AbstractThis work aims at the kinetic studies of the hydrochar produced from hydrothermal carbonization of citrulluslanatus(watermelon) peel. The hydrochar was prepared at optimized conditions regarding Carbon content, High Heating Value and Yield at experimental conditions of 210 °C and 1 h operation. The Watermelon peel hydrocharkineticswereinvestigated at heating rates of 5 °C${\text{mi}}{{\text{n}}^{ - 1}}$, 10 °C${\text{mi}}{{\text{n}}^{ - 1}}$, 15 °C${\text{mi}}{{\text{n}}^{ - 1}}$, &amp; 20 °C${\text{mi}}{{\text{n}}^{ - 1}}$, through thermogravimetric analysis. Two iso-conversional models were applied to compute the kinetic parameters and pyrolysis behavior of hydrochar. The kinetic study using Kissinger-Akahira-Sunose (KAS) model revealed that for a conversion range of 0.1 to 0.8,the activation energy was observed to be in the range of 146 to 220 kJ/mol. Similarly, the activation energies estimated through Flynn-Wall-Ozawa (FWO) model also gave a similar range of kinetic energies from 147 to 219 kJ/mol. Moreover, higher pre-exponential factor values explained the convoluted structure of biomass. The regression coefficient (${R^{2\,}}$) for both the models is high and they have shown similar activation energies which confirms that the best reaction mechanism is predicted. This research helps in establishing an economical and efficient technology for producing clean bioenergy and useful chemicals.

Optimization, Kinetic and thermodynamic studies of MiLd steel corrosion in different soils

Response Surface Methodology (RSM) based on the central composite rotatable design was used to determine the optimum conditions for the corrosion rate of mild steel in three different soils viz; Clay, Loamy and Sandy soils. The parameters Time (1-3 hours) and Temperature (303-313K) were assessed as controlling factors for the investigation of corrosion rate of mild steel in the different soils. The result shows the optimum corrosion rate of 54, 48 and 40 gm-2day-1 for Clay, Loamy and Sandy soils respectively obtained at time 2.5hr and temperature of 387.5K. A quadratic equation was obtained by multiple regression analysis for predicting the optimisation of the corrosion rate of mild steel in the different soils. This study also investigated the effect of temperature within the range of 298-383K on the corrosion rates on mild steel in Clay, Loamy and Sandy soils using weight loss method. It was observed that as temperature increases the corrosion rate also increases. The kinetic functions in terms of the pre-exponential factor, (A) was found to be 247.3984, 295.0073 and 171.0575 and the activation energy (Ea) 5.2045, 6.1856, 5.4623 for clay, loamy and sandy soil respectively. A high activation energy and low pre-exponential factor implies a low corrosion rate hence sandy soil showed minimum corrosion rate. The thermodynamic function in terms of ∆H, ∆S, and ∆G were studied using the Arrhenius and Transition state equations respectively. The result showed that the corrosion process in the soils is endothermic and the reaction is spontaneous at 298, 323 and 383K.

Catalytic transesterification to biodiesel at room temperature over several solid bases

The transesterification activity of several solid base catalysts in biodiesel production was systematically studied and evaluated at room temperature. Commercialized calcined silicates showed stronger transesterification ability than other commonly-used oxides, and provided considerable biodiesel yields. Biodiesel yield of >96% was obtained for Na2SiO3 catalyst (calcined at 400 °C) at 28 °C within 12 h with methanol/oil molar ratio of 12/1 and catalyst dosage of 5 wt%, and for CaSiO3 catalyst (calcined at 550 °C) at 28 °C within 24 h with methanol/oil molar ratio of 27/1 and catalyst dosage of 23 wt%. The high activity of Na2SiO3 came from low activation energy of 104.6 kJ/mol and considerable higher pre-exponential factor of 3.73 × 1015 min−1, which produced high turnover frequency of 0.234 min−1 at 28 °C. The introduction of CA-O-Si structure in CaSiO3 resulted in high surface basicity of 0.70 mmol/g and high pre-exponential factor of 3.79 × 1019 min−1 but high activation energy of 136.4 kJ/mol. The loss of catalyst activity was mainly due to the variation of surface silicate structure during transesterification.

Oxidative dehydrogenation of methanol at ceria-supported vanadia oligomers

We study the adsorption and partial oxidation of methanol at a trimeric VOX species supported on ceria, which was found to be the thermodynamically most stable species under slightly reducing conditions. Results for the oxidation of methanol obtained using dispersion-corrected PBE+U and HSE are compared with a metastable monomeric VO2 species. The intrinsic barriers for monomers (103kJ/mol), trimers (133kJ/mol), and the pristine surface (136kJ/mol) are compared with the corresponding values derived from temperature-programmed desorption experiments, i.e. 100, 125, and 150kJ/mol, respectively. It was found that the VO2 trimer is more active than the pristine ceria (111) surface due to entropic effects, showing up in a higher pre-exponential factor. However, the VO2 trimer is less active than the monomer due to structural relaxation in the surface O layer of the latter.

Thermal decomposition of 2,4,6-triazidopyrimidine in the melt

The kinetics and the products of thermal decomposition of 2,4,6-triazidopyrimidine in the melt were investigated by thermogravimetry, manometry, mass-spectrometry, and IR spectroscopy. The kinetic and activation parameters of the processes were found. Nitrogen was the only gaseous product of the reaction. The structure of the solid reaction product was determined. A mechanism of thermal decomposition of 2,4,6-triazidopyrimidine, including elimination of a nitrogen molecule to give nitrene in the initial step, was proposed. The unusually high pre-exponential factor in the Arrhenius equation (1016.7±0.7 s–1) was attributed to a significant contribution of polymerization (polycondensation) to the overall process, resulting in the formation of carbon—nitrogen two-dimensional networks.

Structure-modulated ionic transport behavior in zirconia–dysprosia mixed oxides

In the present study, we report a systematic study on Zr1−xDyxO2−x/2 system exploring the effect of structure on ion-transport. All the compositions were synthesized by combustion route followed by high-temperature sintering and thoroughly characterized by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and AC impedance studies. These studies revealed a phase relation wherein Zr0.9Dy0.1O1.95 exhibited coexistence of a monoclinic and cubic phase. The Dy3+ content greater than 10 mol% led to complete stabilization of cubic zirconia solid solutions. The structural evolution has also been monitored with Raman spectroscopy wherein very weak pyrochlore-type ordering in compositions with x ≥ 0.4 could be observed even when XRD showed a fluorite-type structure. The effect of structure-induced conductivity control was revealed by AC impedance analysis which bestowed a high ionic conductivity, 0.0048 Scm−1 at 700 K, on the nominal composition Zr0.8Dy0.2O1.90. This has been attributed to a very high disorder prevailing in this system due to the substitution of Zr4+ by Dy3+. It was revealed that the ionic conductivity behavior was driven by high pre-exponential factor which led to substantially high ionic conductivity for Zr0.8Dy0.2O1.90 despite almost equal activation energies observed for all the nominal compositions studied. Such high ionic conductivity for a zirconia-based system makes it a potential candidate for electrolyte for intermediate-temperature solid oxide fuel cell, as they are inherently stabler than ceria-based electrolytes.

Influence of Sm3+ doping on microstructure and electrical properties of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7

( Nd 0.7 Yb 0.3)2 Zr 2 O 7 and (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 (0 &lt; x ≤ 0.25) ceramics have been synthesized by pressureless sintering by tailoring the chemical compositions. Microstructure and electrical conductivity of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and AC impedance spectroscopy. ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 ceramic exhibits a mixed crystal structure of defect fluorite and pyrochlore. After doping with Sm 3+ cations, the structure changes from a mixed type of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 to a single pyrochlore type of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7, as the addition of Sm 3+ reduces the difference in ionic radius between Nd 3+ and Yb 3+. However, (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 ceramics contain the localized short-range disorder despite the structural order overall in the pyrochlore. The measured total conductivities of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 obey the Arrhenius relation. Doping of Sm 3+ enhances the electrical conductivity of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 ceramic significantly, which is closely related to the variations in the concentration of oxygen vacancies at 48f sites, relatively low activation energy and high pre-exponential factor caused by the long-range order and short-range disorder.

Increase in grain boundary ionic conductivity of Li1.5Al0.5Ge1.5(PO4)3 by adding excess lithium

Abstract Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this work, it was synthesized using solid-state reaction with an excess amount of Li to improve grain boundary ionic conductivity. The additional Li improved grain boundary conductivity even though the relative density decreased. This improvement may originate from a beneficial characteristic of grain boundary induced by the segregation of some of Li to the grain boundary. This segregation was indirectly observed by the change of morphology of particles in samples with excess Li. The segregation of Li may result in a facile Li transport in grain boundaries, as indicated by low activation energy and a high pre-exponential factor of the grain boundary conductivity. Through improving grain boundary conductivity with excess Li, a high total ionic conductivity of 1.9 × 10 − 4 S·cm − 1 is achieved at room temperature even with a low relative density of 78%. This porous and high ionic conducting solid electrolyte can be useful in configuring the electrode composite of all-solid-state cells.