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CdS-PVP nanocomposites grown with various concentrations of Cd + /S − and PVP are studied using Raman and atomic force microscopy mapping on same selected areas. The study shows that CdS nanocrystals are embedded in either a thin-film or spheres of PVP, formation of which depends on relative ratio of Cd + /S − concentration (density of nanocrystals) to PVP. Collapse of PVP from planer matrix to the sphere morphology is correlated with high density of CdS nanocrystals and the attractive interaction between CdS nanocrystals and PVP polymer leading to a co-operative growth mechanism. The understanding developed can be used to control the growth of CdS-PVP nanocomposites with desired properties for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

The doping effects of a small amount of RE (Gd and Ho) atoms at A (La) sites of La 2 NiMnO 6 double perovskite have been studied by preparing the materials using mechanical alloying of oxide powders and thermal treatment (800–1200 °C), and a direct sintering of the oxide powders at 1300 °C. The synchrotron x-ray diffraction patterns have been used to confirm the formation of single (monoclinic) phase or bi-phased lattice structure depending on thermal treatment temperature. The bi-phased samples are consisting of primary monoclinic phase (P 2 1 /n space group) and secondary orthorhombic phase (Pnma space group). The x-ray photoelectron spectroscopy has confirmed the presence of trivalent La, RE ions, and mixed-valence state of Ni and Mn ions in the samples. The existence of bi-phasic lattice structure and mixed-valence state of Ni and Mn ions have determined magnetic properties. The monoclinic phase has shown ferromagnetic Curie point around 280 K, which has been reduced to low temperature by Gd and Ho doping. The orthorhombic phase has shown weak ferro/ antiferromagnetic spin ordering temperature around 150 K. The experimental results in RE doped La 2 NiMnO 6 double perovskite support a strong correlation between lattice structure and magnetic properties, which depend on doping of RE ions at A sites, electronic charge state of Ni and Mn ions, structural phase components and anti-site disorder of Mn/Ni ions at octahedral sites. • Synthesis of Gd/Ho doped La 2 NiMnO 6 by mechanical alloying and solid state sintering. • A detailed analysis of structure, charge state of ions, and heat treatment effects on magnetism. • The heat treatment effect on coexisting monoclinic and orthorhombic phases in the samples. • Role of Ni-O-Mn bond structure and doping effect on ferromagnetic superexchange interactions. • Role of chemical inhomogeneity on bi-phased ferromagnetic properties and short range order. [ABSTRACT FROM AUTHOR]

The low temperature lattice structure and magnetic properties of Co 2.75 Fe 0.25 O 4 ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 473–1173 K. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 473–873 K. The samples annealed at temperatures 973 K and 1173 K (CF90) have shown single phased lattice structure. Refinement of the neutron diffraction patterns in the measurement temperature range 5–300 K confirmed the antiferromagnetic (AFM) Co 3 O 4 and ferrimagnetic (FIM) Co 2.75 Fe 0.25 O 4 phases for the sample annealed at 873 K and single FIM phase of Co 2.75 Fe 0.25 O 4 for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples. • A detailed study is presented on lattice structure and magnetic properties. • Single-phased and two-phased lattice structure are identified in spinel oxide. • Ferrimagnetic properties are enhanced in spinel oxide close to Co 3 O 4. • The effects of AFM and ferrimagnetic clusters are seen in the temperature scale. • Multiple magnetic transitions are observed in no-equilibrium spinel structure. [ABSTRACT FROM AUTHOR]

Hexagonal Sr 0.6 Ba 0.4 MnO 3 (SBMO) follows P 6 3 / mmc symmetry where MnO 6 octahedra are both face-shared (Mn 2 O 9 bioctahedra) and corner-shared via oxygen anion. It undergoes ferroelectric (FE) and antiferromagnetic (AFM) orderings close to the room temperature. Magnetic properties appear to be governed by intricate exchange interactions among Mn4+ ions within and in adjacent Mn 2 O 9 bioctahedra, contingent upon the local structural changes. Calculations based on our model spin-Hamiltonian reveal that the dominant linear AFM fluctuations between the Mn4+ ions of two oxygen-linked bi-octahedra result in short range correlations, manifest as a smooth drop in magnetization below 325 K. Competition between spin-exchange and local-strain is reckoned as responsible for the atypical magneto-electricity, obtained near the room temperature. • An incipient ferroelectric (FE) with magnetic anomaly nearby room temperature. • Improper-FE is owed to the locally-unequal Mn–O bond lengths in the MnO 6 octahedra. • Short range stabilization of dipoles with short range magnetic ordering. • Mn-displacement soft-vibration mode is coupled to the spin ordering in the material. • Frustration involving spin-exchange and local-strain is responsible for the ME. [ABSTRACT FROM AUTHOR]

Abstract Sm 6 UO 12 has been synthesized by urea-combustion method and characterized using synchrotron x-ray source. The compound is found to be in single phase crystallizing in rhombohedral lattice with lattice parameters a = 10.153 Å and c = 9.625 Å. High-pressure experiment at ambient temperature reveals the lattice to be stable up to 27.0 GPa. The bulk modulus of the compound is found to be 157.0 GPa. At higher pressures, reflections broaden out as a result of disorder in the system, leading to amorphization at further higher pressures. High pressure and high temperature (HP-HT) x-ray diffraction studies have been carried out up to 6.0 GPa and 673 K. A softening is seen in the material at HP-HT resulting in lower bulk modulus at high temperature. Volume thermal expansion coefficients are found to be 22 × 10−6 K−1 and 17.7 × 10−6 K−1 in the temperature range 298 K–473 K and 298 K-673 K, respectively. Highlights • The compressibility in RE 6 UO 12 is found to increase along Rare-earth series. • Contrary to temperature effect, a -axis is more rigid under pressure than c -axis. • Disorder in anions followed by that of cations is seen at high pressures. • Decrease in thermal expansion coefficient with respect to pressure is observed. [ABSTRACT FROM AUTHOR]

In the present contribution, structural and magnetic properties of Pulsed laser deposited (PLD) Co 2 FeGa (CFG) thin films have been studied as a function of substrate temperature. Structural investigation carried out by X-Ray Diffraction (XRD) measurement reveals mixed phase cubic structure of the films which changes from a nearly ordered to highly disordered phase with an increase in substrate temperature. Grazing Incidence X-Ray Diffraction (GIXRD) study shows the presence of disordered A2 phase similar to the bulk target. Grazing Incidence X-Ray Reflectivity (GIXR) measurement reveals the formation of bi-layer structure in the films with different density and thickness though the overall thickness remains same. Field Emission Scanning Electron Microscopy (FESEM) study shows the formation of a droplet-like morphology of the films. Extended X-ray Absorption Fine Structure (EXAFS) study serves a major role in complementing the XRD results and also shows a strong hybridization of Co with Ga maintaining the half metallicity. A novel approach in analyzing the EXAFS data additionally gives quantitative estimation of the different kinds of disorders present in the samples at the atomic level. In addition to this, magnetization result suggests that the films grown at lower substrate temperatures acts as proper ferromagnet following the well known spin wave theory with higher value of spontaneous magnetization in comparison to other samples. A lesser value of saturation magnetization in the films compared to bulk also supports the presence of antisite disorders. [ABSTRACT FROM AUTHOR]

Understanding the microscopic origin of physical properties is fundamental to the study of glasses. In the present study, unique trends were observed in structural and dynamical properties in lead-borate [ x PbO:(1- x )B 2 O 3 ] glasses upon increasing the modifier. Properties driven by short-range structural changes like, glass transition temperature ( T g ) and elastic modulii exhibit a broad maxima around x = 0.3, in congruence with the average coordination number < r >. Using Raman spectroscopy, this behaviour is attributed to the gradual conversion of three-coordinate ( B 3 ) to four-coordinate ( B 4 ) boron species. However, dynamic properties like the Boson peak and fragility behave similar to the above structural properties except an anomalous dip at x = 0.3. The corresponding dynamic correlation length, therefore, exhibits a decrease except a peak at x = 0.3 with increasing x . The static correlation lengths estimated from the first sharp diffraction peak (FSDP), did not follow a linear trend with the dynamic correlation lengths, indicating a different spatial origin. The analysis of the Boson peak and FSDP suggests that while the Boson peak arises from intermediate-range ordering within the network units, the FSDP arises due to ordering of voids between such units. Moreover, the Boson peak maximum showed a linear decrease with increasing < r >, while the Boson peak position and fragility were found to vary linearly. These correlations emerge from the evolution of the network packing and connectivity with the addition of modifier and changing role of lead oxide as a glass former at higher concentrations. The anomalous variation in dynamical properties reflects the critical role of Pb 2+ in tuning the intermediate-range structure of the vitreous network. [ABSTRACT FROM AUTHOR]

Resonant photoemission spectroscopy has been used to investigate the character of Fe 3 d states in FeAl alloy. Fe 3 d states have two different character, first is of itinerant nature located very close to the Fermi level, and second, is of less itinerant (relatively localized character), located beyond ∼2 eV below the Fermi level. These distinct states are clearly distinguishable in the resonant photoemission data. Comparison between the results obtained from experiments and first principle based electronic structure calculations show that the origin of the itinerant character of the Fe 3 d states is due to the ordered B 2 structure, whereas the relatively less itinerant (localized) Fe 3 d states are from the disorders present in the sample. The exchange splitting of the Fe 3 s core level peak confirms the presence of local moment in this system. It is found that the itinerant electrons arise due to the hybridization between Fe 3 d and Al 3 s and 3 p states. Presence of hybridization is observed as a shift in the Al 2 p core-level spectra as well as in the X-ray near edge absorption spectra towards lower binding energy. Our photoemission results are thus explained by the co-existence of ordered and disordered phases in the system. [ABSTRACT FROM AUTHOR]

We have synthesized the Co 1.75 Fe 1.25 O 4 spinel ferrite by chemical reaction of Co and Fe nitrates at alkaline medium. We have annealed the as-prepared material up to 1100 °C to study the changes in lattice structure and magnetic properties. We have used synchrotron X-ray diffraction and Raman spectroscopy to identify the lattice structure. The material formed a composite spinel structure of Co rich phase (20–30%) and Fe rich phase (80–70%) for annealing temperature range 200–800 °C, and single phased spinel structure at 900 °C. At annealing temperature 1100 °C, the sample showed minor amount of hematite phase, in addition to two spinel phases. All the samples are ferrimagnetic in nature, but ferrimagnetic properties in mixed-phased samples are distinctly different from single phased sample. The analysis of the temperature and magnetic field dependence of magnetization data revealed a wide distribution of exchange interactions, anisotropy barriers, blocking of magnetic domains, and exchange bias for the samples having multi-phase components. On the other hand, single phased sample has shown the highest magnetization and the smallest coercivity with lowest distribution of magnetic exchange energy and anisotropy. [ABSTRACT FROM AUTHOR]

The spinel oxide Co 2.25 Fe 0.75 O 4 has been prepared by co-precipitation route. The as prepared material has been annealed at 800 °C under vacuum. Properties of the samples annealed under vacuum have been compared with the sample annealed in air. Synchrotron X-ray diffraction, Raman spectroscopy and X-ray absorption near edge structure spectroscopy have been used for structural phase characterization. The cubic spinel structure in air annealed sample has been splitted into Co and Fe rich phases. The Co rich spinel phase has transformed into Cobalt monoxide (CoO) after vacuum annealing. This has resulted an increase of Fe:Co ratio in the Fe rich spinel phase. Raman spectra indicated a transformation of the distribution of Co and Fe ions from normal spinel like structure for the sample annealed in air to mixed spinel structure for the samples annealed under vacuum. The existence tetravalent Fe 4+ ion has been confirmed in all the samples and it is new information for Co doped spinel ferrite system. All the samples exhibited ferrimagnetic behavior and exchange bias effect. The focus point is that vacuum annealing has been used as an effective route of material processing to control the structural phase and also, enhancement of magnetic properties in Co rich ferrite. [ABSTRACT FROM AUTHOR]

In the present work, important information on crystalline structure and band offset of InAs/Ge heterojunction epitaxially grown directly on Ge (111) substrate is presented. As revealed by high resolution x-ray diffraction (HRXRD) and Raman measurements the InAs nanostructures are highly crystalline and oriented with the substrate having predominantly zinc-blende (ZB) structure. The relaxation ratio of grown layer is of 95%. The lateral and vertical coherence lengths are estimated to be ∼65 nm and ∼14 nm, respectively, which closely match with atomic force microscopy results. As revealed from HRXRD experiments, two domains/sub-lattices of ZB InAs (111) structures having different stacking configurations were found to coexist. A band diagram is constructed for InO/InAs/Ge system. Valence band offset of 300 meV and conduction band offset of 20 meV for InAs/Ge have been determined. Hence, InAs/Ge (111) system can have potential application in low power devices. [ABSTRACT FROM AUTHOR]

The present work summarizes the effect of irradiation on the microstructure of Zr–1 wt.% Nb fuel cladding alloy using 5 MeV proton beam from a Variable Energy Cyclotron. The correlation between the damage energy deposition profile and the consequent microstructural modification has been obtained for different irradiation doses employing detailed line profile analysis of wide angle and Synchroton grazing incidence X-ray diffraction data. The inhomogeneous microstructure resulting from ion irradiation as a function of depth could be analyzed by these techniques. The size of the coherent domains was found to decrease drastically upon irradiation together with an increase in the microstrain values within these domains. A progressive decrease in the domain size, with a corresponding increase in the microstrain, was noticed upon increasing the dose of irradiation and along the depth of the irradiated samples. [ABSTRACT FROM AUTHOR]

The structural and light emission properties of calcium tungstate (CaWO 4) nanoparticles containing Eu3+ and Dy3+ are studied. CaWO 4 nanoparticles were prepared by chemical routes followed by drying at 80°C, doping with 1, 3, 5, 7 and 10 mol% of Eu 2 O 3 and/or Dy 2 O 3 and final annealing at 800oC. The samples were characterized by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), synchrotron X-ray diffraction (XRD), Raman and photoluminescence (PL) spectroscopy. FE-SEM studies show that CaWO 4 sample dried at 80°C contains spherical particles of diameter ∼5 μm, and upon annealing at 800°C, dense and irregular shaped structures are formed. EDS mapping found a uniform distribution of Eu and Dy ions and only a small segregation in the CaWO 4 matrix is observed. XRD studies revealed the co-existence of the tetragonal CaWO 4 and cubic Dy 2 O 3 and/or Eu 2 O 3 phases in the doped samples and rule out the replacement of Ca2+ by rare-earth ions. The structural parameters: crystallite size, lattice strain, unit cell dimensions, atomic position coordinates, bond-lengths, bond-angles and cation-oxygen coordination numbers were determined. The short-range structure of CaWO 4 consists of interconnected CaO 8 and WO 4 units. All the W–O bonds in WO 4 units have the same length whereas two types of Ca–O bond-lengths exist in CaO 8 units. The undoped CaWO 4 sample annealed at 800°C, has the smallest Ca–O bond-lengths and unit cell dimensions due to the compressive macrostrain induced by heat-treatment. On incorporating Eu3+ and Dy3+, the W–O and Ca–O bond-lengths increase slightly. Raman spectra of all the samples are similar and show W–O vibrational modes. PL studies found that the undoped CaWO 4 , Eu and Dy-doped CaWO 4 samples emit blue, red and yellow light respectively. The co-doped sample: 2 mol% Eu 2 O 3 –5 mol% Dy 2 O 3 –CaWO 4 was closest to the ideal white light emission properties. • Structure-property correlations in Eu 2 O 3 /Dy 2 O 3 and CaWO 4 composite samples. • Eu and Dy ions expand CaWO 4 lattice. • 3-Mol% Eu 2 O 3 gives maximum luminescence in CaWO 4. • Luminescence intensity decreases with increase in Dy 2 O 3 from 1 to 10 mol%. • Eu and Dy co-doping in CaWO 4 produces white light emission. [ABSTRACT FROM AUTHOR]

UZr 2 has been synthesized using the arc-melting technique. At ambient the compound is found to crystallize in a modified C32 , AlB 2 type structure, called δ-structure and it remains stable up to 20 GPa. However, an anomalous decrease of c/a ratio has been observed in different pressure intervals at ambient temperature. At elevated temperature c/a ratio, shows a marginal increase with pressure. The bulk modulus and its pressure derivative at ambient temperature are found to be 108.3 GPa and 5.0, respectively. High-pressure and high-temperature studies reveal a softening in the material at higher temperatures. The thermal expansion coefficients are found to decrease from 4.6 × 10−5 K−1 at 1.2 GPa to 2.7 × 10−5 K−1 at 6.6 GPa in the temperature range 300 K–473 K. • Bulk modulus of UZr 2 is 108.3 GPa at ambient & 101.6 GPa at 473 K indicating softening at high temperature. • Anomaly in rate of c/a @ P is due to strengthening of U - Zr covalent bond along the ' a ' axis at higher pressures. • c/a ratio is found to increase marginally in HP-HT experiments as compared to near-constant c/a in HP experiments. • A usual decrease in the thermal expansion coefficient, is observed in the temperature range 300 K–473 K. [ABSTRACT FROM AUTHOR]

Electron-irradiation induced changes in structural and, magnetic properties of Co 57.6 Fe 14.4 Si 4.8 B 19.2 Nb 4 , Fe 72 Si 4.8 B 19.2 Nb 4 and, Co 72 Si 4.8 B 19.2 Nb 4 metallic glasses were studied using magnetic hysteresis and, synchrotron X-ray diffraction measurements. Results reveal composition dependent changes of magnetic properties in electron irradiated metallic glasses. A low electron irradiation dose (15 kGy) enhances saturation magnetization (up to 62%) in Fe-based alloy (Fe 72 Si 4.8 B 19.2 Nb 4 ). Synchrotron XRD measurements reveal that electron irradiation transforms the amorphous matrix to a more ordered phase, accountable for changes in magnetic properties. [ABSTRACT FROM AUTHOR]