Room Temperature X-ray Diffraction Research Articles

Structural, magnetic and transport properties of FeRuVZ (Z = Si, Ge) Heusler alloys: Experiment and theory

Heusler alloys based on 4d-elements are relatively less explored though they are known to host interesting electronic/magnetic properties useful for future spintronics applications. Here, we report a comparative study of the structural and magnetic properties of FeRuVSi (FRVS) and FeRuVGe (FRVG) using experimental and theoretical tools. Magneto-transport measurements have also been carried out to probe the role of magnetism on their transport behaviour. Room temperature (T) X-ray diffraction data reveals cubic crystal structure (space group No. 216) with B2 type antisite disorder between Fe and Ru sites in both the alloys. They show ferromagnetic behaviour below the Curie temperature (TC) 84 K for FeRuVSi and 57 K for FeRuVGe respectively. The field dependence of magnetization at low-T shows saturating (nearly saturating) behaviour for FRVS (FRVG). Transport measurements show metallic behaviour with a sharp reduction in the resistivity near TC. Ab-initio calculations predict nearly half metallic behaviour with ∼ 87 % and ∼ 89 % spin polarization for FRVS and FRVG in their ordered states. The inclusion of antisite disorder changes the magnetic configuration, leading to a visible decrease in the magnetic moment and spin polarization. The calculated net moment and the transport properties agree fairly well with those observed experimentally. These results confirm the importance of disorder in determining the intrinsic properties of these alloys. Such combined studies help in the identification of more novel quantum materials suitable for future spintronic applications.

Synthesis and Properties of the Ba2PrWO6 Double Perovskite.

We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.

Electrical resistivity and magnetoresistance of Sr3Fe2+xMo1–xO9–3x/2 (x = 0.45, 0.60, and 1.00) prepared by the solid-state reaction

In this paper, we focus on understanding the behavior of the temperature dependence of electrical resistivity (ρ) and magnetoresistance (MR) in Sr3Fe2+xMo1–xO9–3x/2 perovskites with x = 0.45, 0.60, and 1.00. Three polycrystalline materials were synthesized using conventional solid-state reaction techniques. Rietveld analysis of room-temperature X-ray diffraction data reveals that all three compositions crystallize in tetragonal symmetry; where x = 0.45 and 0.60 undergo an I4/mcm space group, while x = 1.00 adopts a P4/mmm space group. Electrical resistivity measurements carried out at magnetic fields (0 and 1 T) reveal the presence of a transition from the ferromagnetic phase to the paramagnetic phase in the vicinity of the TMI. The metal-insulator transition temperature (TMI) decreases with increasing Fe content and rises slightly with changing magnetic field from 0 to 1 T. The magnetoresistance (MR) of the SrFeO3–δ sample (x = 1.00) has a large value of about 63.6 %, indicating that it can be exploited for certain devices. A variety of theoretical models are used to study the behavior of electrical resistivity in various temperature ranges, showing excellent agreement with experimental results.

Anomalous Nernst effect and thermal conductivity in Co3Sn2S2 polycrystals

A polycrystalline sample of Co3Sn2S2 shandite was synthesized using spark plasma sintering for its densification. The unit cell parameters, a = 5.3688(1) Å and c = 13.1797(1) Å, refined from room temperature X-ray diffraction data, confirm the R-3m shandite structure. The frustrated nature of the Co magnetic network is invoked to explain the low effective paramagnetic moment of Co, μeff = 1.04μB/Co, whereas the ferromagnetic Curie temperature, TC = 175K, determined from T-dependent magnetic susceptibility corresponds to the metal to metal transition at that temperature. Interestingly, the residual resistivity ratio and resistivity values indicate that the electronic transport is driven by the in-plane contribution. This behaviour close to that of ab-plane transport of Co3Sn2S2 crystal fits well with the measurement of an anomalous Nernst effect (ANE). The latter reaches at T = 100K a maximum value Sxy = +1.5 μV K−1, i.e. a reduction by a factor of ≈2 as compared to crystal, explained by the reduction for the magnetization, M, of the former. This is also demonstrated by the H-dependent Sxy and M loops that match very well. Similarly, a hysteresis is found for the thermal conductivity demonstrating the existence of an anomalous thermal Hall effect of about 5 % of the total thermal conductivity. This study shows that ANE can be also measured in ceramics of Weyl ferromagnets.

Synthesis of a scheelite barium molybdate: Structural, topological, electrical, and transport properties for negative temperature coefficient thermistor application

Preliminary structural analysis of Scheelite barium molybdate BaMoO4 (BMO) ceramic using NTREOR-09 and McMaille methods has confirmed the tetragonal symmetry with room temperature X-ray diffraction (XRD) spectrum. Further, other structural parameters like crystallite size and compressive lattice strain are found to be of 31 nm and −0.00151 respectively. The topographical study of scanning electron microscope (SEM) image confirms the polycrystalline nature with no other impurities in the sample. Detailed analysis of dielectric permittivity (εr), and loss (tanδ) supports Maxwell-Wagner and Koop's phenomena. The non-overlapping small polaron tunnelling (NSPT) and correlated barrier hopping (CBH) model have emphasis on transport mechanism. The presence of semiconducting behavior of the scheelite material at various temperatures and frequencies examined by complex impedance and modulus spectra. The value of grain resistance decreases as temperature increases demonstrating the existence of negative temperature coefficient (NTCR) behavior of the material. The increase of the value of thermistor constant (β) (67.339, 516.613, and 772.485 in the different high-temperature range) suggests an efficient application of the material for NTC-thermistor.

Tuning of the magneto-caloric effects in Ni43Mn46In11 magnetic shape memory alloys by substitution of boron

In this study, we report the structural, magnetic, and magnetocaloric properties of B substitution on the Mn site in Ni43Mn46−x B x In11(x = 0.5, 1.0) Heusler alloys. Crystal structure analysis using room-temperature x-ray diffraction data reveals both samples have mixed phases composed of cubic and tetragonal phases. The structural and magnetic phase transition characteristic temperatures are determined using differential scanning calorimetry, isothermal magnetization (MT), and isofield magnetization (MH) measurements. Both alloys exhibit inverse and direct magnetocaloric effects in the vicinity of their magnetostructural transition and Curie temperature (T C), respectively. For Ni43Mn45.0B1.0In11 a maximum magnetic entropy change of 25.06 J kg−1 K−1 is observed at 250 K for a magnetic field change of 5 T.

Observation of weak ferromagnetism in the antiferromagnetic host and large electronic heat capacity in β-Mn-type structured Mn3Al alloy

Numerous interesting features of antiferromagnets open up the possibility of designing new antiferromagnetic materials that can be useful for spintronic device applications. Here we present the structural, magnetic, thermal and electrical transport properties of polycrystalline Mn3Al alloys prepared by arc melting. Rietveld refinement of the room temperature X-Ray diffraction patterns reveals that the arc-melted Mn3Al crystallizes in a β Mn phase (space group 213). Detailed analysis of the magnetic data suggests for a dominant antiferromagnetic ordering. However, an in-homogenous magnetic disorder is observed in the system having a weak ferromagnetic phase in the antiferromagnetic host. In spite of the strong spin fluctuations in this system, the signature of spin glass-like nature in these alloys are not observed as probed by the frequency-dependent AC-Susceptibility measurements. Furthermore, the heat capacity was insensitive to the applied field of 3 Tesla with a negligible magnetic contribution suggesting a large electronic contribution to the heat capacity in these alloys. This work provides a useful insight into the tunable physical properties of the Heusler alloys for exploring antiferromagnetic based spintronic applications.

Dependence of Electrochemical Characteristics of a Biodegradable Fe-30Mn-5Si wt.% Alloy on Compressive Deformation in a Wide Temperature Range

Fe-30Mn-5Si alloy subjected to a compression test at various deformation temperatures ranging from 350 to 900 °C with a strain rate of 1 s−1 are studied. It was found that the Fe-30Mn-5Si alloy exhibits high resistance to the dynamic recrystallization process in a whole studied range of deformation temperatures. There are no differences in structure formation in the zone of action of tangential tensile stresses and peripheral and central zones of localized compressive stresses. The room-temperature X-ray diffraction study shows the presence of a single-phase state (FCC γ-austenite) after deformation temperature range from 350 to 700 °C and a two-phase state (FCC γ-austenite + HCP ε-martensite) after deformation test at 900 °C. The presence of a two-phase state provides a higher rate of biodegradation compared with a single-phase state. The changes in the biodegradation rate dependence on the structure change with an increase in the deformation temperature are explained. Favorable temperature regimes for subsequent thermomechanical processing are proposed based on the relationship between structure formation and biodegradation rate to obtain semi-products from the Fe-30Mn-5Si alloy.

Composition dependent structural and dielectric properties of (Bi0.5Na0.5TiO3)(1-x)-(KNb0.9Ta0.1O3)x ceramic

In the present study, pellet samples of (Bi0.5Na0.5TiO3)(1-x)-(KNb0.9Ta0.1O3)x were prepared using mixed oxide, solid-state reaction method. The ‘x’ value was changed from 0.00 to 0.10 at the gap of 0.01. Room temperature X-Ray Diffraction (RT-XRD) measurements and Rietveld refinement were carried out to examine the structural properties of the prepared compositions. The observed RT-XRD data indicated the rhombohedral phase, for compositions with ‘x’ value 0.00 to 0.03. However, rhombohedral and tetragonal phases were present in compositions with ‘x’ values 0.04 to 0.10. The room temperature dielectric measurements of the synthesized compositions were carried out at different frequencies ranging from 1 kHz to 1 MHz. Dielectric measurements showed the composition dependency. Moreover, we have found anomalies in the compositions with 0.04 ≤ x ≤ 0.10.

Structural and electrical properties of PLZT x/65/35 ceramics prepared via mechanical activation method near the morphotropic phase boundary

This paper reports the effect of lanthanum addition on the structural and electrical properties of (Pb1-xLax)(Zr0.65Ti0.35)O3 (PLZT x/65/35, x = 8%,10%,12%,15%) ceramics near the morphotropic phase boundary. Studies were conducted on the PLZT x/65/35 ceramics synthesized via a combinatorial approach of high-energy ball milling (mechanical activation method) followed by Cold Isostatic Pressing (CIP). Due to the application of CIP, PLZT ceramics exhibited improved density and a closely packed microstructure. The SEM analysis showed that PLZT x/65/35 ceramics exhibited an increase in grain size with higher concentrations of La3+ ions. Room temperature X-ray diffraction results revealed the formation of perovskite PLZT phase. The investigation on temperature-dependent dielectric, ferroelectric properties of PLZT x/65/35 ceramics provided experimental confirmation of structures cited in XRD analysis. Among all the compositions, PLZT 8/65/35 samples showed a well saturated, uniform P–E hysteresis loop with a high remanent polarization (Pr). Poled PLZT 8/65/35 samples displayed electric field induced large strains with limited hysteresis. Piezoelectric charge coefficients (d33), electromechanical coupling factors (kp, k33, k31) were determined for poled PLZT x/65/35 ceramics and it was found that PLZT 8/65/35 ceramics reveal properties superior to other compositions. Furthermore, the unipolar strain, Pr, d33, kp, k33, k31 values of PLZT 8/65/35 composition exceeded the previously reported ones for the same composition prepared via sol-gel synthesis technique.

Layered Monoclinic Perrierite Oxo-Silicate La4Mn5Si4O22+Δ: A New Interstitial Oxide Ion Conductor for Low Temperature Applications

Oxide-ion conductors are important for various energy applications such as solid oxide fuel cells, solid oxide electrolyser cells, oxygen separation membranes, oxygen sensors, etc. State-of-the-art stable oxygen active materials often have adequate oxygen ion diffusion and chemical surface exchange only at high temperatures (> 700 oC). A promising strategy to improve the oxygen ion transport is to use the interstitial oxygen ion conductors as the interstitial diffusion barriers are often lower than vacancy-mediated diffusion barrier, potentially enabling reduced operation temperatures. However, due to the large size of the oxide ion, the formation of an adequate concentration of interstitials is difficult and hence the number of interstitial oxygen conductors is currently limited to just a handful of compounds, e.g., Ruddlesden-Popper, apatite, melilite, scheelite, fluorite and disordered hexagonal perovskites.We screened a large number of oxide materials using high-throughput ab initio methods (Please see separate poster from Jun Meng on this screening) and predicted stable formation and fast diffusion of interstitial oxygen in a new class of material La4Mn5Si4O22+δ (LMS), motivating us to synthesize this material and experimentally study its oxide ion transport properties. The room temperature X-ray diffraction study followed by Rietveld refinement confirmed its layered monoclinic perrierite structure. Electron probe micro-analysis (EPMA) and iodometric titration revealed the presence of the hyper stoichiometric oxygen anion (δ ~ + 0.5) confirming the interstitial oxygen ions within LMS lattice. Thermogravimetric analysis showed a small mass increment in LMS when heated at high temperatures suggesting the high temperature stability of interstitial oxygen ions. The measured ionic conductivity of LMS is higher than the yttria stabilized ZrO2, perovskite oxide La1-xSrxCo1-yFeyO3 and Ruddlesden-Popper oxide materials. Electrical conductivity relaxation studies demonstrated that self-diffusion and surface exchange coefficients of oxygen ion are comparable to or higher than many state-of-the-art oxide ion conductors. Finally, the high temperature stability of the synthesised material was confirmed using X-ray diffraction after each measurement.Overall, this experimental study confirms computational predictions that layered perrierite LMS is a new class of interstitial oxide ion conductors and suggests our overall approach may help the rational design of interstitial mediated oxide ion conductors-based devices suitable for efficient and stable applications at low temperature.

Effects of bismuth substitution on the structural and ionizing radiation shielding properties of the novel BaSn1-xBixO3 perovskites: An experimental study

In this study, BaSn1-xBixO3(0.00 ≤ x ≤0.20) polycrystalline perovskites are synthesized using the conventional solid-state reaction method for their utilization as materials for shielding against ionizing radiation. The Rietveld refinement of the room temperature X-ray diffraction (XRD) pattern revealed that all samples exhibited a cubic structure with Pm3‾m space group. To investigate the photon shielding properties of the prepared samples, the mass attenuation coefficient (MAC) was experimentally measured, and then the findings were benchmarked with the calculated results from the XCOM database. The obtained experimental results showed a reasonable correlation with the XCOM data, with relative differences in the mass attenuation coefficient ranging from 0.57% to 7.1%. Based on the measured MAC, different radiation shielding parameters such as the linear attenuation coefficient (LAC), half-value layer (HVL), mean free path (MFP), transmission factor (TF), and radiation protection efficiency (RPE) were calculated for all ceramics studied. These findings suggest that BaSn1-xBixO3(0.00 ≤ x ≤0.20) ceramic samples could be beneficial for use in shielding applications against ionizing radiation.

Sol-gel synthesis and Opto-electrical properties study of double perovskite oxide Dy2NiMnO6 thin film

Thin film of double perovskite oxide Dy2NiMnO6 (DNMO) has been synthesised by the simple and cost-effective chemical solution deposition technique. The room temperature X-ray diffraction pattern and Raman spectroscopy confirm the monoclinic (space group - P21/n) crystal structure of polycrystalline DNMO thin film. The optical and electrical properties of DNMO thin film are investigated to study the detailed photo physical properties of DNMO thin film. The direct band gap and temperature dependant impedance spectroscopy confirm its semiconductor behaviour. Impedance spectroscopy also shows two types of dielectric relaxation behaviour and the nature of conductivity reveals the electron hopping conduction mechanism. Moreover, the chemical solution deposited DNMO film shows promising photo response under white light.

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices.

Substantial enhancement in magnetic and magnetodielectric properties of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite

In pursuit of room-temperature magnetoelectric materials for numerous technological applications various materials are vigorously explored. Such is the motivation behind the synthesis of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite. The phase purity and structural analysis are examined through Rietveld refinement of room temperature X-ray diffraction (XRD) pattern, which shows that the composite has ‘Pbam + Pbnm’ phases. X-ray photoelectron spectroscopy confirmed the presence of mixed valence state of magnetic ions i.e. Fe2+ (41%), Fe3+ (45%), Fe4+ (14%) and Mn2+ (88%), Mn3+ (12%) favouring superexchange and double exchange interactions contributing to enhanced magnetizations. The presence of weak ferromagnetism in the composite is confirmed by large irreversibility in ZFC-FC data, isothermal magnetization curves and Arrott plots throughout the wide temperature range (10–300 K). High value of coercivity (Hc) is observed with an increase in temperature which indicates magnetic anisotropy in the system. Along with that, a plausible magnetodielectric (MD) coupling is evidenced in temperature dependent dielectric (ε′) and tan loss. Later, it is verified through intrinsic MD results carried out at higher frequency. At room temperature, the MD effect is found to be ∼2%. A contrasting behaviour in magnetic field variation of MD% is at 10 K and 300 K. However, a butterfly-shaped MD curve is evidenced where MD% ∼0.21% at 10 K. Lastly, Landau free energy expression confirmed that MD effect emerges from the coupling term ‘γP2M2′ where γ is ∼1.6 × 10−2 (emu/g)−2 and ∼1.1 × 10−2 (emu/g)−2 at 10 K and 300 K respectively. Thus, the above findings highlight the significance of the composite as a potential room temperature magnetoelectric material for device applications.

Molecular dynamics and thermo physical properties of solid catanionic surfactants composed of octadecyltrimethylammonium bromide and n-alkanoic acids

Two mixed surfactants comprising cationic octadecyltrimethylammonium bromide CH3(CH2)17N+(CH3)3Br− (C18TAB) modified with dodecanoic C12H24O2 (DDA) or hexadecanoic C16H32O2 (HDA) acids have been studied in the solid state in a wide temperature range (25–150 °C). The molecular dynamics and thermotropic properties of acid-modified asymmetric DDA-C18TAB and symmetric HDA-C18TAB surfactants were investigated using DSC measurements and temperature-variable FTIR spectroscopy complemented by room-temperature powder X-ray diffraction. XRD showed a formation of a new layered compound, the acid-modified C18TAB mixed surfactant comprising a hydrophobic moiety formed by two alkyl chains of different lengths. DSC measurements revealed the difference in thermal behavior between symmetric and asymmetric mixed surfactants showing successive phase transitions and several polymorphs in the solid state. With FT-IR spectroscopy, the phase transitions seen in DSC were identified as related to subtle lattice rearrangements in the low-temperature phases C1C2, the trans-gauche conformational disorder and rotational motions of methylene chains followed with lattice instabilities in the intermediate phases C3 and C4, and finally rotational disorder of the alkyl chains and the ionic layer in the high temperature phase H. For the first time, the stabilization effect of DDA acid on the bilayer structure of C18TAB was found.

A simple goniometer-compatible flow cell for serial synchrotron X-ray crystallography.

Serial femtosecond crystallography was initially developed for room-temperature X-ray diffraction studies of macromolecules at X-ray free electron lasers. When combined with tools that initiate biological reactions within microcrystals, time-resolved serial crystallography allows the study of structural changes that occur during an enzyme catalytic reaction. Serial synchrotron X-ray crystallography (SSX), which extends serial crystallography methods to synchrotron radiation sources, is expanding the scientific community using serial diffraction methods. This report presents a simple flow cell that can be used to deliver microcrystals across an X-ray beam during SSX studies. This device consists of an X-ray transparent glass capillary mounted on a goniometer-compatible 3D-printed support and is connected to a syringe pump via light-weight tubing. This flow cell is easily mounted and aligned, and it is disposable so can be rapidly replaced when blocked. This system was demonstrated by collecting SSX data at MAX IV Laboratory from microcrystals of the integral membrane protein cytochrome c oxidase from Thermus thermophilus, from which an X-ray structure was determined to 2.12 Å resolution. This simple SSX platform may help to lower entry barriers for non-expert users of SSX.

Structural and magnetic quantification of rhombohedral – Orthorhombic phase transition in gadolinium substituted bismuth ferrite

Room-temperature X-ray diffraction (XRD), and High-resolution transmission microscopy (HR-TEM) were used to investigate the structural properties of multiferroic Bi1-xGdxFeO3 perovskites, (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30). The system under investigation was synthesized through a citric acid-based auto-combustion technique. XRD analysis revealed that the pure bismuth ferrite and the gadolinium substituted bismuth ferrite up to x = 0.10 samples composed of a polycrystalline rhombohedral structure (space group R3c (161)), the samples with Gd concentration between x = 0.15 and x = 0.25 show coexistence of rhombohedral and orthorhombic phases. At the same time, Bi0.7Gd0.3FeO3 crystallizes in a pure orthorhombic structure (space group Pbnm (62)). The crystallographic parameters and the ratio of the two competed phases were estimated using Rietveld refinement of XRD data. Williamson-Hall model based on the refined XRD data was used to estimate the average crystallite length and the induced lattice strain. Furthermore, TEM and HR-TEM images coincident with the XRD results. Bi1-xGdxFeO3 nanoparticles display coupling interactions between weak ferromagnetism and canted antiferromagnets at room temperature. The magnetic properties were estimated by analyzing the M(H) hysteresis loops collected using a vibrating sample magnetometer (VSM). This study can sustain new strategies for tailoring new smart materials with different fascinating properties.

Role of Fe3+ doping vis-à-vis secondary phases on the electrical transport of LiTi2(PO4)3 solid electrolyte

Fast ion conducting solid-electrolytes, with diverse technological applications, have been studied critically in recent years. Among various prototype structures, NASICON structured materials are known for their comparatively high bulk conductivities, which could be further improved by selective substitution at cationic sites. Present work reports the effect of Fe3+ doping at the Ti4+ sites vis-à-vis secondary phases on the ionic conductivity of NASICON structured lithium titanium phosphate (LiTi2(PO4)3 or LTP) solid electrolyte. Li1+xTi2−xFex(PO4)3 (x = 0.0, 0.1 and 0.2) was synthesized using the solid-state reaction method. Crystal structure, morphology, chemical composition, and ionic conductivity were studied using room-temperature powder X-ray diffraction (p-XRD), field emission scanning (FESEM) and high-resolution transmission (HRTEM) electron microscopy, and temperature-dependent impedance spectroscopy. Very low bulk activation energies were found for all the samples, attributed to interstitial diffusion via a concerted migration. The room-temperature ionic conductivity initially increased upon Fe3+ doping (x = 0.1) and dropped subsequently (x = 0.2). The aberrant growth of electrolyte grains, associated gas pores, and cracks formed during sintering were successfully reduced by the LiTiOPO4 phase formation upon Fe doping, initially raising the grain boundary conductivity. However, doped samples also showed segregation of another secondary phase, Li2FeTi(PO4)3, whose larger weight fraction at x = 0.2 severely restricted the Li-ion migration resulting in sudden conductivity loss. These results suggest the need to optimise the microstructure, especially the amount of secondary phases, which contribute to the grain boundary resistance, affecting the ionic conductivity of the samples.

Structural, electronic, and magnetic properties of CoFeVGe-based compounds: Experiment and theory

We have carried out a combined theoretical and experimental investigation of both stoichiometric and nonstoichiometric CoFeVGe alloys. In particular, we have investigated CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe bulk alloys. Our first principles calculations suggest that all four alloys show ferromagnetic order, where CoFeVGe, Co1.25Fe0.75VGe, and Co0.75Fe1.25VGe are highly spin polarized with spin polarization values of over 80%. However, the spin polarization value of CoFe0.75VGe is only about 60%. We have synthesized all four samples using arc melting and high-vacuum annealing at 600 °C for 48 hours. The room temperature x-ray diffraction of these samples exhibits a cubic crystal structure with disorder. All the samples show single magnetic transitions at their Curie temperatures, where the Curie temperature and high field (3T) magnetization are 288 K and 42 emu/g; 305 K and 1.5 emu/g; 238 K and 39 emu/g; and 306 K and 35 emu/g for CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe, respectively.