Single-Atomic Co-N4 Sites with CrCo Nanoparticles for Metal-Air Battery-Driven Hydrogen Evolution.

Designing highly active and robust earth abundant trifunctional electrocatalysts for energy storage and conversion applications remain an enormous challenge. Herein, we report a trifunctional electrocatalyst (CrCo/CoN4@CNT-5), synthesized at low calcination temperature (550 °C), which consists of Co-N4 single atom and CrCo alloy nanoparticles and exhibits outstanding electrocatalytic performance for the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The catalyst is able to deliver a current density of 10 mA cm-2 in an alkaline electrolytic cell at a very low cell voltage of ∼1.60 V. When the catalyst is equipped in a liquid rechargeable Zn-air battery, it endowed a high open-circuit voltage with excellent cycling durability and outperformed the commercial Pt/C+IrO2 catalytic system. Furthermore, the Zn-air battery powered self-driven water splitting system is displayed using CrCo/CoN4@CNT-5 as sole trifunctional catalyst, delivering a high H2 evolution rate of 168 µmol h-1. Theoretical calculations reveal synergistic interaction between Co-N4 active sites and CrCo nanoparticles, favoring the Gibbs free energy for H2 evolution. The presence of Cr not only enhances the H2O adsorption and dissociation but also tunes the electronic property of CrCo nanoparticles to provide optimized hydrogen binding capacity to Co-N4 sites, thus giving rise to accelerated H2 evolution kinetics. This work highlights the importance of the presence of small quantity of Cr in enhancing the electrocatalytic activity as well as robustness of single-atom catalyst and suggests the design of the multifunctional robust electrocatalysts for long-term H2 evolution application.

Coupling Single-Ni-Atom with Ni-Co Alloy Nanoparticle for Synergistically Enhanced Oxygen Reduction Reaction.

Developing nonprecious metal-based oxygen reduction reaction (ORR) electrocatalysts with superior activity and durability is crucial for commercializing proton-exchange membrane (PEM) fuel cells. Herein, we report a metal-organic framework (MOF)-derived unique N-doped hollow carbon structure (NiCo/hNC), comprising of atomically dispersed single-Ni-atom (NiN4) and small NiCo alloy nanoparticles (NPs), for highly efficient and durable ORR catalysis in both alkaline and acidic electrolytes. Density functional theory (DFT) calculations reveal the strong coupling between NiN4 and NiCo NPs, favoring the direct 4e- transfer ORR process by lengthening the adsorbed O-O bond. Moreover, NiCo/hNC as a cathode electrode in PEM fuel cells delivered a stable performance. Our findings not only furnish the fundamental understanding of the structure-activity relationship but also shed light on designing advanced ORR catalysts.

Role of C and B4C barrier layers in controlling diffusion propagation across the interface of Cr/Sc multilayers.

The optical performance of low-bilayer-thickness metallic multilayers (ML) can be improved significantly by limiting the intermixing of consecutive layers at the interfaces. Barrier layers are supposed to exhibit a decisive role in controlling diffusion across the interfaces. The element-specific grazing incidence extended X-ray absorption fine structure technique using synchrotron radiation has been used in conjunction with grazing incidence X-ray reflectivity and diffuse X-ray scattering measurements to study the impact of the two most common barrier layers, viz., C and B4C, at the interfaces of Cr/Sc MLs. The diffusion propagation is reduced by both the barrier layers; however, it is found that the improvement is more significant with the B4C barrier layer. It is seen that C forms an intermixed layer with Sc and leads to carbide formation at the interface, which then acts as shielding and prevents further interdiffusion, while B4C hardly penetrates into Sc and stops the overlap between Sc and Cr directly by wetting the corresponding interface. Thus, the above measurements reveal crucial and precise information regarding the elemental diffusion kinetics at the interfaces of Cr/Sc MLs in a non-destructive way, which is very important for technological applications of these MLs as X-ray optical devices.

Comprehensive study on the origin of orthorhombic phase stabilization in Gd-doped HfO2 and DFT calculations.

In recent times, ultra-thin films of hafnium oxide (HfO2) have shown ferroelectricity (FE) attributed to the orthorhombic (o) phase of HfO2 with space group Pca21. This polar o-phase could be stabilized in the doped thin film of the oxide. In the present work, both polar and non-polar o-phases of HfO2 could be stabilized in Gd-doped bulk polycrystalline HfO2. Rietveld analysis of XRD data shows that the relative population of o-phases in the presence of the monoclinic (m) phase of HfO2 increases with increasing Gd-content. The local environment around the host atom has been investigated by time differential perturbed angular correlation (TDPAC) spectroscopy, synchrotron based X-ray near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements showed a reduction in grain size with increasing Gd-dopant indicating a solute drag effect. It could be established that the segregation of the Gd-dopant in the grain boundary is a thermodynamically favorable process and the solute drag effect plays an important role in nucleation of the o-phase in bulk HfO2. Stabilization of Gd in both Pbca and Pca21 phases of HfO2 was supported by defect formation energy calculations using density functional theory (DFT). The present study has important implications in future applications of HfO2 in ferroelectric devices and in understanding the role of dopants in stabilizing the o-phase of HfO2 in the bulk.

Clinical perspectives, immunohematologic insights, and transfusion management in IgA-associated autoimmune hemolytic anemia.

Autoimmune hemolytic anemia (AIHA) due to warm-reacting IgA autoantibodies is rare. Here, we explored the clinical and immunohematologic characteristics of patients suffering from IgA-associated warm AIHA (WAIHA) and their transfusion management. The 9-year study included 214 patients with WAIHA who were further classified into two groups: (1) IgA-associated WAIHA and (2) non-IgA-associated WAIHA. Clinical and laboratory details were obtained from patient files and the Hospital Information System. All immunohematologic investigations were performed following standard operating procedures and established protocols. Among the 214 patients with WAIHA, 17 (7.9%) belonged to the IgA-associated group; of these, two IgA-only WAIHA cases were found. The mean hemoglobin in this group was 5.58 g/dL, and 15 (88.2%) of these patients received a total of 32 units of packed red blood cell (RBC) transfusions. In vivo hemolytic markers were significantly abnormal in the IgA-associated WAIHA group when compared with the non-IgA group. Secondary WAIHA was found in 11 (64.7%) patients with IgA-associated WAIHA. Patients with IgA-associated WAIHA received more blood transfusions than individuals in the non-IgA group (p = 0.0004). A total of 17 (7.9%) patients with WAIHA experienced adverse events to blood transfusion. Detailed characterization of WAIHA with particular emphasis on IgA-associated and non-IgA-associated WAIHA is essential to evaluate the disease characteristics, access the degree of hemolysis, understand the immunohematologic behaviors of the antibodies, and manage blood transfusions.

Interface modification of Cr/Ti multilayers with C barrier layer for enhanced reflectivity in the water window regime.

The influence of a carbon barrier layer to improve the reflectivity of Cr/Ti multilayers, intended to be used in the water window wavelength regime, is investigated. Specular grazing-incidence X-ray reflectivity results of Cr/Ti multilayers with 10 bilayers show that interface widths are reduced to ∼0.24 nm upon introduction of a ∼0.3 nm C barrier layer at each Cr-on-Ti interface. As the number of bilayers increases to 75, a multilayer with C barrier layers maintains almost the same interface widths with no cumulative increase in interface imperfections. Using such interface-engineered Cr/C/Ti multilayers, a remarkably high soft X-ray reflectivity of ∼31.6% is achieved at a wavelength of 2.77 nm and at a grazing angle of incidence of 16.2°, which is the highest reflectivity reported so far in the literature in this wavelength regime. Further investigation of the multilayers by diffused grazing-incidence X-ray reflectivity and grazing-incidence extended X-ray absorption fine-structure measurements using synchrotron radiation suggests that the improvement in interface microstructure can be attributed to significant suppression of inter-diffusion at Cr/Ti interfaces by the introduction of C barrier layers and also due to the smoothing effect of the C layer promoting two-dimensional growth of the multilayer.

Insight into the charging-discharging of magnetite electrodes: in situ XAS and DFT study.

The structural changes of Fe3O4 nanoparticle electrodes in Li ion batteries during charging-discharging cycles have been investigated using in situ X-ray absorption spectroscopy (XAS). Chemometric methods viz., Principal Component Analysis (PCA) and Multivariate Curve Resolution-Alternate Least Square (MCR-ALS) have been used for analysis of the in situ XANES data during the charge-discharge cycle, which help to identify the various species formed during the lithiation-delithiation of Fe3O4. The concentration variation of the different species has also been determined and the detailed intercalation-conversion mechanism of the Fe3O4 electrodes during the first discharge has been established. Subsequently, the first charge and second discharge cycles were also studied to apprehend the difference in redox reaction between the first discharge and subsequent cycles. The above studies clearly identify the four species involved in the whole intercalation-conversion process of Fe3O4 electrode of a Li ion battery and also indicate the irreversibility of the conversion reaction in subsequent cycles which may be one of the reasons for capacity fading of these electrodes. The above results have also been corroborated with density functional theory (DFT)based ab inito calculations.

Probing the solute-drag effect and its role in stabilizing the orthorhombic phase in bulk La-doped HfO2 by X-ray and gamma ray spectroscopy.

The recent observation of ferroelectricity in ultra thin films of hafnium oxide (HfO2) has been attributed to the orthorhombic (o) phase of HfO2 with space group Pca21. Although this oxide is polymorphic in nature, this polar o-phase is known to be stabilized in the doped thin film oxide. The objective of the present experiment is to stabilize the o-phases in La doped bulk polycrystalline HfO2 and investigate their evolution with the doping concentration through Time Differential Perturbed Angular Correlation (TDPAC), X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) measurements. The present work reports the presence of both the polar Pca21 phase and the antipolar Pbca phase at different La-concentrations. Two o-phases of HfO2 with space groups Pca21 and Pbca, difficult to distinguish by other complimentary methods, could be unambiguously identified by utilizing the atomic scale sensitivity of the electric field gradient (EFG) embedded in TDPAC spectroscopy. The determination of the oxidation state and the local environment of La-atoms by XANES and EXAFS measurements illuminates the microscopic role of the dopant in stabilizing the o-phase. The "solute drag model" proposes a critical crystallite size for the nucleation of the o-phase in bulk HfO2 and explains the role of the La-dopant in stabilizing the o-phase. Thus the present study shows the possibility of stabilizing the polar o-phase and hence attaining ferroelectricity in bulk HfO2 to augment the scope of future application for this ferroelectric device.

Exhaled nitric oxide as a guiding tool for bronchial asthma: A randomised controlled trial.

BACKGROUND: Evidence regarding the role of non-invasive marker of airway inflammation, fractional exhaled nitric oxide (FeNO) to guide asthma treatment is equivocal. We aimed to evaluate if the use of FeNO to adjust inhaled corticosteroid treatment resulted in reduced daily corticosteroid use and lesser exacerbations. METHODS: 100 patients of bronchial asthma in the age group of 12-70 years were randomised to receive inhaled corticosteroids based on either FeNO measurements (n = 50) or as per Global Initiative for Asthma (GINA) guidelines. Follow up was done every 2 months for period of 12 months. Results were compared in terms of mean daily inhaled corticosteroid use and number of exacerbations. RESULTS: After the follow up period of 12 months, mean daily dose of ICS (SD) required in FeNO group was 267.5 µg (126.29), as opposed to control group in which mean daily dose of steroid was 320.00 µg (138.69). However this observed difference in steroid dose was statistically insignificant (p value = 0.061). The estimated mean (SD) rate of asthma exacerbation experienced in follow up period of 12 months in FeNO group was 0.3 episodes (0.54) per patient per year (95% confidence interval, 0.145-455) and 0.4 episodes (0.61) per patient per year in control group (95% confidence interval, 0.228-572). However this difference in rate of exacerbations between the two study groups was not statistically significant (p = 0.387). CONCLUSION: FeNO guided management strategy for asthma did not result in statistically significant reduction in dose of inhaled corticosteroids or number of asthma exacerbations.

Operando X-ray absorption spectroscopy study of the Fischer-Tropsch reaction with a Co catalyst.

This article describes the setting up of a facility on the energy-scanning EXAFS beamline (BL-09) at RRCAT, Indore, India, for operando studies of structure-activity correlation during a catalytic reaction. The setup was tested by operando X-ray absorption spectroscopy (XAS) studies performed on a Co-based catalyst during the Fischer-Tropsch reaction to obtain information regarding structural changes in the catalyst during the reaction. Simultaneous gas chromatography (GC) measurements during the reaction facilitate monitoring of the product gases, which in turn gives information regarding the activity of the catalyst. The combination of XAS and GC techniques was used to correlate the structural changes with the activity of the catalyst at different reaction temperatures. The oxide catalyst was reduced to the metallic phase by heating at 400°C for 5 h under H2 at ambient pressure and subsequently the catalytic reaction was studied at four different temperatures of 240, 260, 280 and 320°C. The catalyst was studied for 10 h at 320°C and an attempt has been made to understand the process of its deactivation from the XANES and EXAFS results.

First results from the XMCD facility at the Energy-Dispersive EXAFS beamline of the Indus-2 synchrotron source.

Setting up of the X-ray Magnetic Circular Dichroism (XMCD) measurement facility with hard X-rays at the Energy-Dispersive EXAFS beamline (BL-08) at the Indus-2 synchrotron source is reported. This includes the design and development of a water-cooled electromagnet having a highest magnetic field of 2 T in a good field volume of 125 mm3 and having a 10 mm hole throughout for passage of the synchrotron beam. This also includes the development of an (X-Z-θ) motion stage for the heavy electromagnet for aligning its axis and the beam hole along the synchrotron beam direction. Along with the above developments, also reported is the first XMCD signal measured on a thick Gd film in the above set-up which shows good agreement with the reported results. This is the first facility to carry out XMCD measurement with hard X-rays in India.

Structural studies of spray pyrolysis synthesized oxygen deficient anatase TiO2 thin films by using X-ray absorption spectroscopy.

The present work focuses on synthesis and X-ray absorption studies of single phase oxygen deficient anatase TiO2 thin films. These films are prepared in a two-step method viz. the synthesis of near stoichiometric anatase TiO2 films using an open atmospheric spray pyrolysis method followed by vacuum annealing at their corresponding synthesis temperatures (Ts = 450 °C, 500 °C) for different time durations (t = 2, 4, 6, 8 hours). XRD and Raman studies of these films ascertained the formation and retention of the anatase phase post annealing, indicating that there was no phase change due to prolonged annealing. Extended X-ray absorption spectra (EXAFS) and X-ray absorption near edge spectra (XANES) revealed the presence of an oxygen vacancy and its effect on the local co-ordination. The co-ordination number obtained from EXAFS analysis revealed that the number density of the oxygen vacancy is higher in the case of thin films synthesized at 450 °C than in the case of the films synthesized at 500 °C. As the oxygen vacancy leads to changes in local co-ordination, which in turn have a profound effect on the pre-edge features of the X-ray absorption spectra (XAS), theoretically simulated XAS spectra of pure anatase TiO2 and oxygen deficient anatase TiO2 were generated using FEFF and were found to match with the experimentally observed spectra. In addition, the ambiguities in whether a change in the metal-oxygen bond length has any effect on the pre-edge features or not were delineated in the present study by comparing the pre-edge peak positions of the oxygen deficient TiO2 films. Our results matched with those of some of the researchers who have studied the rutile phase TiO2, wherein it was concluded that in the case of the titanium-oxygen system, the mean Ti-O bond length does have an effect on the pre-edge peak position. It was observed that as the Ti-O mean bond length increases, the pre-edge peak positions shift towards lower energy, which is in concurrence with the literature available for other Ti-O systems with similar geometry. The second pre-edge peak intensity, which is a measure of disorder, is higher for TiO2450 °C-2 h and TiO2500 °C-2 h thin films. This is attributed to the annealing effect, which suggests that TiO6 octahedrons are the most disordered for thin films annealed for 2 h and become more ordered upon annealing for longer times.

Oxygen vacancy mediated cubic phase stabilization at room temperature in pure nano-crystalline zirconia films: a combined experimental and first-principles based investigation.

We report here the stabilization of the cubic phase under ambient conditions in the thin films of zirconia synthesized by electron beam evaporation. The cubic phase stabilization was achieved without the use of chemical stabilizers and/or concurrent ion beam bombardment. Films of two different thicknesses (660 nm and 140 nm) were deposited. While the 660 nm as-deposited films were in the cubic phase, as indicated by X-ray diffraction and Raman spectroscopy, the 140 nm as-deposited films were amorphous and the transformation to the cubic phase was obtained after thermal annealing. Extended X-ray absorption fine structure measurements revealed the existence of oxygen vacancies in the local structure surrounding zirconium for all films. However, the amount of these oxygen vacancies was found to be significantly higher for the amorphous films as compared to that for the films in the cubic phase (660 nm as-deposited and 140 nm annealed films). The stabilization of the cubic phase is attributed to the breaking of the oxygen-zirconium bonds due to the presence of the oxygen vacancies, which results in the suppression of the soft X2- mode of vibration of the oxygen sub-lattice. Our first-principles modeling under the framework of density functional theory shows that the cubic structure with oxygen vacancies is indeed more stable under ambient conditions than its pristine (without vacancies) counterpart due to breaking of the oxygen bonds. The requirement of a critical amount of these vacancies for cubic phase stabilization is discussed.

Doping effect on the local structure of metamagnetic Co doped Ni/NiO:GO core-shell nanoparticles using X-ray absorption spectroscopy and the pair distribution function.

Core-shell nanoparticles of Co (0%, 3%, and 5%) doped Ni/NiO and incorporated (5 mg) graphene oxide (GO) sheets were synthesized by a sol-gel auto-combustion method. X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and pair distribution function measurements were employed for the determination of the local structure and structural properties of the samples. Due to the effect of Co doping the bond lengths of all coordinate atoms were varied. The microstructural features in the core-shell structured particles were evaluated with high-resolution transmission electron microscopy (HRTEM). Magnetic properties of the samples revealed that both the interface of Ni/Co and NiO crystal lattices and the weight fraction of Ni have significant impact on their magnetic properties at 5 K to 300 K. Experimental results show that Co doping and GO incorporation into Ni/NiO suppress the antiferromagnetic charge ordering and lead to a spin-flop metamagnetic behavior at 5 K to 300 K temperatures. Above 5 K, the step-like transitions transform into broad ones. This step-like feature is correlated with the collapse of the balance between the magnetic energy and elastic energy at the core-shell interface. It is confirmed from M-T measurements that the blocking temperature of Ni/NiO was reduced with Co content.

Effect of pretreatment with organic solvent on enzymatic digestibility of cauliflower wastes.

The present study investigated the operational conditions for different pretreatment approaches and subsequent enzymatic hydrolysis of cauliflower wastes (stalk and leaf) for better release of fermentable sugars. The structural analysis of raw and pretreated lignocellulosic biomasses was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transforms infrared (FTIR) analysis. Results demonstrated that the highest cellulose conversion rate and removal of most of the hemicellulose and lignin were obtained with organosolvent pretreatment. Using methanol in presence of sodium (Na) acetate was most effective in delignification of cauliflower wastes. In the present study, methanol (100% v/v) in presence of 0.1 M Na-acetate at 121 °C for 45 and 60 min for stalk and leaf, respectively, gave maximum reducing sugar yield. Response surface methodology was used to optimize different process parameters for enzymatic saccharification using microbial cellulase and xylanase. The optimum operation condition of enzymatic hydrolysis of organosolvent pretreated cauliflower wastes were substrate loading (2.5% w/v for both stalk and leaf), enzyme loading (15 and 10 U/g for stalk and leaf, respectively), pH (4.46 and 5.48 for stalk and leaf, respectively), at 60 °C and for 180 min.

Phosphorus recovery from the sludge generated from a continuous bipolar mode electrocoagulation (CBME) system.

Phosphorus is known to be a limited non-renewable resource. Phosphorus is obtained from phosphate rock, which is likely to be depleted in the next few decades. Therefore, it is very important to find alternate sources of phosphorus from which phosphorus can be recycled and recovered. This study focuses on the recovery of phosphorus from the sludge generated from a continuous bipolar mode electrocoagulation (CBME) system, used for treating a palm oil mill effluent (POME). The sludge generated from the CBME system is leached with oxalic acid and sulphuric acid for phosphorus recovery with and without thermal treatment. Acid leaching was carried out at various time intervals using various liquid/solid (L/S) ratios of acids and sludge. The CBME system caused a 73% removal of phosphorus from POME, where phosphorus is precipitated in sludge as iron phosphates or adsorbed as phosphates depending on the pH in the system. Acid leaching resulted in nearly 85% recovery of phosphorus with both sulphuric acid and oxalic acid for sludge combusted at 900 °C. Statistical analysis was carried out to find the significance of the operational conditions on the phosphorus yield. Acid leaching results in the formation of orthophosphates, which can be used as a raw material for synthesis of chemical fertilizers.

Survivors of deliberate self-harm attempt in the military milieu: An exploratory study of psychiatric morbidity and psychosocial correlates.

BACKGROUND: Deliberate self-harm (DSH) is common in modern society. A million people worldwide die from suicide each year, leading to a large toll on human resources and economy. Research has revealed DSH as an important indicator of eventual suicide worldwide. The present study focused on DSH attempters among Armed Forces personnel and family members with the aim of identifying modifiable factors to provide recommendations for primary prevention in the military milieu. METHODS: Hundred cases of survivors of DSH were evaluated in a case-control study using psychiatry assessment instruments (the Mini-International Neuropsychiatric Interview, Pierce Suicide Intent Scale, Hamilton's Depression and Anxiety Scales and presumptive life event scale) to assess psychiatric morbidity and psychosocial correlates. The findings were compared with those of 100 healthy matched controls. The data were analysed using SPSS software. RESULT: The majority of DSH survivors (98%) had concurrent psychiatric morbidity, major depressive disorder (23%) being the commonest diagnosis followed by psychotic disorder and alcohol use disorder. Presence of relationship problems (69%) and financial difficulties (19%) were significant triggering factors in our study. Many DSH attempters had voiced suicidal ideation (66%) before their act and had history of aggression or violence (76%) in the past. CONCLUSION: Our findings are discussed in relation with findings in the literature. Recommendations regarding awareness campaign, specific skill development programs and the need for early intervention in individuals with psychiatric morbidity have been proposed to prevent such behaviours.

Impact of previous hepatitis B infection on the clinical outcomes from chronic hepatitis C? A population-level analysis.

Chronic coinfection with hepatitis C virus (HCV) and hepatitis B virus (HBV) is associated with adverse liver outcomes. The clinical impact of previous HBV infection on liver disease in HCV infection is unknown. We aimed at determining any association of previous HBV infection with liver outcomes using antibodies to the hepatitis B core antigen (HBcAb) positivity as a marker of exposure. The Scottish Hepatitis C Clinical Database containing data for all patients attending HCV clinics in participating health boards was linked to the HBV diagnostic registry and mortality data from Information Services Division, Scotland. Survival analyses with competing risks were constructed for time from the first appointment to decompensated cirrhosis, hepatocellular carcinoma (HCC) and liver-related mortality. Records of 8513 chronic HCV patients were included in the analyses (87 HBcAb positive and HBV surface antigen [HBsAg] positive, 1577 HBcAb positive and HBsAg negative, and 6849 HBcAb negative). Multivariate cause-specific proportional hazards models showed previous HBV infection (HBcAb positive and HBsAg negative) significantly increased the risks of decompensated cirrhosis (hazard ratio [HR]: 1.29, 95% CI: 1.01-1.65) and HCC (HR: 1.64, 95% CI: 1.09-2.49), but not liver-related death (HR: 1.02, 95% CI: 0.80-1.30). This is the largest study to date showing an association between previous HBV infection and certain adverse liver outcomes in HCV infection. Our analyses add significantly to evidence which suggests that HBV infection adversely affects liver health despite apparent clearance. This has important implications for HBV vaccination policy and indications for prioritization of HCV therapy.

Local crystal structure in the vicinity of Cr in doped AlN thin films studied by X-ray absorption spectroscopy.

This article reports the detailed X-ray absorption spectroscopy (XAS) study of Al1-xCrxN (x = 4, 6, 11%) thin films synthesized by the reactive magnetron co-sputtering technique. All these films were crystallized with a hexagonal wurtzite structure with preferential orientation along the a-axis without the formation of any secondary phases. Surface chemical analysis to evaluate the Cr concentration was carried out using X-ray photoelectron spectroscopy. The study confirmed the presence of AlN and Cr in bonding with N. The local crystal structure around the Cr dopant in the as-synthesized and annealed thin films has been analyzed by both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. From XAS, it was found that Cr replaced the Al atom in the AlN lattice and led to a localized CrN species with distorted tetrahedral AlN in the absence of Cr clustering. The bond lengths of (Cr-N)ax, (Cr-N)bs and Cr-Al, extracted from the EXAFS fitting, were found to decrease with the Cr concentration for both the as-synthesized and annealed thin films due to the enhancement of p-d hybridization between the dopant and the host atoms. However, in the annealed 11% Cr film, the bond lengths are larger than the other and tend to match the Cr-N geometry in CrN.

Unraveling doping induced anatase-rutile phase transition in TiO2 using electron, X-ray and gamma-ray as spectroscopic probes.

The present work reports the microscopic details of anatase (A) to rutile (R) phase transformation in a Mn-doped TiO2 system. Titanium dioxide (TiO2) powder was synthesized at three different dopant percentages, namely 1, 5, and 10 atom% of Mn, by a coprecipitation technique. Time differential perturbed angular correlation (TDPAC) spectroscopy was used to identify the formation of the rutile-like phase (R*) during the phase-transition process and revealed interface nucleation to be promoted by the Mn dopant. Electron paramagnetic resonance (EPR) spectroscopy, synchrotron-based X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) studies showed that Mn exhibited a mixed valence states of 2+ and 4+ at different stages of the annealing process. The rutile onset temperature gradually decreased with the increase in the Mn content. The present report proposes the mechanism for the phase transformation and details the effect of Mn on the A to R phase-transformation process. This can assist in gaining a fundamental understanding of the A to R phase-transformation process and the role of the dopant in stabilizing one phase over the other.