Evidence of Strong Orbital-Selective Spin-Orbital-Phonon Coupling in CrVO_{4}.

Coupling of orbital degree of freedom with a spin exchange, i.e., Kugel-Khomskii-type interaction (KK), governs a host of material properties, including colossal magnetoresistance, enhanced magnetoelectric response, and photoinduced high-temperature magnetism. In general, KK-type interactions lead to deviation in experimental observables of coupled Hamiltonian near or below the magnetic transition. Using diffraction and spectroscopy experiments, here we report anomalous changes in lattice parameters, electronic states, spin dynamics, and phonons at four times the Néel transition temperature (T_{N}) in CrVO_{4}. The temperature is significantly higher than other d-orbital compounds such as manganites and vanadates, where effects are limited to near or below T_{N}. The experimental observations are rationalized using first-principles and Green's function-based phonon and spin simulations that show unprecedentedly strong KK-type interactions via a superexchange process and an orbital-selective spin-phonon coupling coefficient at least double the magnitude previously reported for strongly coupled spin-phonon systems. Our results present an opportunity to explore the effect of KK-type interactions and spin-phonon coupling well above T_{N} and possibly bring various properties closer to application, for example, strong room-temperature magnetoelectric coupling.

A single-step plasma method for rapid production of 2D, ferromagnetic, surface vacancy-engineered MoO3-xnanomaterials, for photothermal ablation of cancer.

A rapid, clean plasma-chemical technique is demonstrated here, for cost-effective, synthesis of surface vacancy engineered, 2D, molybdenum-oxide nanomaterials, during a one-step, integrated synthesis-hydrogenation process for biomedical applications. A laminar plasma beam populated with O and H radicals impinges on a molybdenum target, out of which molybdenum-oxide nanomaterials are very rapidly generated with controlled surface O vacancies. 2D, dark-blue coloured, nano-flake/ribbon like MoO3-xis produced maximum up to 194 g h-1, the core of which still remains as stoichiometric molybdenum-oxide. These nanomaterials can get heated-up by absorbing energy from a near-infrared (NIR) laser, which enable them as photothermal therapy (PTT) candidate material for the invasive precision therapy of cancer. The surface defects endows the products with robust ferromagnetism at room temperature conditions (maximum saturation-magnetization: 6.58 emu g-1), which is order of magnitude stronger than most other vacancy engineered nanomaterials. These nanometric metal-oxides are observed to be perfectly compatible in animal physiological environment and easily dispersed in an aqueous solution even without any pre-treatment. The MoO3-xnanomaterials are stable against further oxidation even under prolonged atmospheric exposure.In vitroexperiments confirm that they have ideal efficacy for photothermal ablation of human and murine melanoma cancer at relatively lower dose. Duringin vivoPTT treatments, they may be manipulated with a simple external magnetic field for targeted delivery at the malignant tumours. It is demonstrated that commensurate to the neutralization of the malignant cells, the nanomaterials themselves get self-degraded, which should get easily excreted out of the body.

Optical temperature sensing by tuning photoluminescence in a wide (visible to near infrared) wavelength range in a Eu3+-doped Bi-based relaxor ferroelectric.

The prevalent material design principles for optical thermometry primarily rely on thermally driven changes in the relative intensities of the thermally coupled levels (TCLs) of rare-earth-doped phosphor materials, where the maximum achievable sensitivity is limited by the energy gap between the TCLs. In this work, a new, to the best of our knowledge, approach to thermometric material design is proposed, which is based on temperature tuning of PL emission from the visible to the NIR region. We demonstrate a model ferroelectric phosphor, Eu3+-doped 0.94(Na1/2Bi1/2TiO3)-0.06(BaTiO3) (NBT-6BT), which, by virtue of the contrasting effects of temperature on PL signals from the host and Eu3+ intraband transitions, can achieve a relative thermal sensitivity as high as 3.05% K-1. This model system provides a promising alternative route for developing self-referencing optical thermometers with high thermal sensitivity and good signal discriminability.

Emergence of metamagnetic transition, re-entrant cluster glass and spin phonon coupling in Tb2CoMnO6.

The double perovskite compound Tb2CoMnO6has been investigated using x-ray absorption spectroscopy (XAS), Raman spectroscopy, magnetic measurements andab initioband structure calculations. It is observed that both anti-ferromagnetic (AFM) and ferromagnetic (FM) phase coexist in this material. The presence of anti-site disorder (ASD) has been established from the analysis of neutron diffraction data. Moreover, a prominent metamagnetic transition is observed in theM(H) behavior that has been explained with the drastic reorientation of the pinned domain which are aligned antiparallel by the antiphase boundaries (APBs) at zero field. The ASD further gives rise to spin frustration at low temperature which leads to the re-entrant cluster glass ∼33 K. The coupling between phononic degree of freedom and spin in the system has also been demonstrated. It is observed that the theoretical calculation is consistent with that of the experimentally observed behavior.

Amorphous Salts Solid Dispersions of Celecoxib: Enhanced Biopharmaceutical Performance and Physical Stability.

Numerous amorphous solid dispersion (ASD) formulations of celecoxib (CEL) have been attempted for enhancing the solubility, dissolution rate, and in vivo pharmacokinetics via high drug loading, polymer combination, or by surfactant addition. However, physical stability for long-term shelf life and desired in vivo pharmacokinetics remains elusive. Therefore, newer formulation strategies are always warranted to address poor aqueous solubility and oral bioavailability with extended shelf life. The present investigation elaborates a combined strategy of amorphization and salt formation for CEL, providing the benefits of enhanced solubility, dissolution rate, in vivo pharmacokinetics, and physical stability. We generated amorphous salts solid dispersion (ASSD) formulations of CEL via an in situ acid-base reaction involving counterions (Na+ and K+) and a polymer (Soluplus) using the spray-drying technique. The generated CEL-Na and CEL-K salts were homogeneously and molecularly dispersed in the matrix of Soluplus polymer. The characterization of generated ASSDs by differential scanning calorimetry revealed a much higher glass-transition temperature (Tg) than the pure amorphous CEL, confirming the salt formation of CEL in solid dispersions. The micro-Raman and proton nuclear magnetic resonance spectroscopy further confirmed the formation of salt at the -S═O position in the CEL molecules. CEL-Na-Soluplus ASSD exhibited a synergistic enhancement in the aqueous solubility (332.82-fold) and in vivo pharmacokinetics (9.83-fold enhancement in the blood plasma concentration) than the crystalline CEL. Furthermore, ASSD formulations were physically stable for nearly 1 year (352 days) in long-term stability studies at ambient conditions. Hence, we concluded that the ASSD is a promising strategy for CEL in improving the physicochemical properties and biopharmaceutical performance.

Magnetoelastic coupling and spin contributions to entropy and thermal transport in biferroic yttrium orthochromite.

Direct engineering of material properties through exploitation of spin, phonon, and charge-coupled degrees of freedom is an active area of development in materials science. However, the relative contribution of the competing orders to controlling the desired behavior is challenging to decipher. In particular, the independent role of phonons, magnons, and electrons, quasiparticle coupling, and relative contributions to the phase transition free energy largely remain unexplored, especially for magnetic phase transitions. Here, we study the lattice and magnetic dynamics of biferroic yttrium orthochromite using Raman, infrared, and inelastic neutron spectroscopy techniques, supporting our experimental results with first-principles lattice dynamics and spin-wave simulations across the antiferromagnetic transition atTN∼ 138 K. Spectroscopy data and simulations together with the heat capacity (Cp) measurements, allow us to quantify individual entropic contributions from phonons (0.01 ± 0.01kBatom-1), dilational (0.03 ± 0.01kBatom-1), and magnons (0.11 ± 0.01kBatom-1) acrossTN. High-resolution phonon measurements conducted in a magnetic field show that anomalousT-dependence of phonon energies acrossTNoriginates from magnetoelastic coupling. Phonon scattering is primarily governed by the phonon-phonon coupling, with little contribution from magnon-phonon coupling, short-range spin correlations, or magnetostriction effects; a conclusion further supported by our thermal conductivity measurements conducted up to 14 T, and phenomenological modeling.

Correlation of dynamical disorder and oxy-ion diffusion mechanism in a Dy, W co-doped La2Mo2O9 system: an electrolyte for IT-SOFCs.

In the present attempt, a Dy, W co-doped La2Mo2O9 (LMX) system is explored to understand the order-disorder phase transition, dynamical disorder state and their influence on the oxy-ion diffusion mechanism. The X-ray diffraction study confirms the co-dopant induced suppression of the order-disorder phase transition temperature of LMX. The oxygen ion diffusion in the LMX matrix is through intrinsic oxygen vacancies. Disorder oxygen vacancies enhance the degree of freedom of oxy-ion diffusion; these are related to the dynamical disorder states in LMX. These disorder states are demonstrated by high temperature Raman spectra. Dynamical disordering of oxygen vacancies in co-doped LMX systems is revealed by studying the rate of change of intensity of the Mo-O bond vibration as a function of temperature; non-uniformity in the rate of change of intensity is correlated to dynamical disorder. The dielectric relaxation studied by using dielectric loss spectra reveals a single relaxation peak for the pure-LMX system, while two dielectric relaxation peaks are revealed for doped LMX systems. Oxygen vacancy reorientation associated with dielectric relaxation is correlated to the diffusion process between O(1) → O(2) and O(1) → O(3) oxygen ion-vacancy exchange sites in doped LMX systems, while it is O(1) through orderly arranged oxygen vacancies in the pure LMX system. To ascertain the relaxation dynamics of the bulk system, electric modulus formalism is helpful, M'' data are fit by the Bergman function represented by the Kohlrausch-Williams-Watts (KWW) formula and non-Debye type relaxation is revealed for all systems. The activation energy of oxy-ion diffusion is reduced by a co-doping effect. Ionic conductivity extracted from complex impedance spectra indicates that oxy-ion conductivity in a co-doped LMX system is improved almost one order as compared to the pure system. The study reveals that a co-doped LMX system has the potential to be used as electrolytes for intermediate temperature solid oxide fuel cells (400-700 °C, IT-SOFCs).

Enhanced Thermoelectric Performance of Novel Reaction Condition-Induced Bi2S3-Bi Nanocomposites.

This is the first report on the enhanced thermoelectric (TE) properties of novel reaction-temperature (TRe) and duration-induced Bi2S3-Bi nanocomposites synthesized using a facile one-step polyol method. They are well characterized as nanorod composites of orthorhombic Bi2S3 and rhombohedral Bi phases in which the latter coats the former forming Bi2S3-Bi core-shell-like structures along with independent Bi nanoparticles. A very significant observation is the systematic reduction in electrical resistivity ρ with a whopping 7 orders of magnitude (∼107) with just reaction temperature and duration increase, revealing a promising approach for the reduction of ρ of this highly resistive chalcogenide and hence resolving the earlier obstacles for its thermoelectric application potentials in the past few decades. Most astonishingly, a TE power factor at 300 K of the highest Bi content nanocomposite pellet, made at 27 °C using ∼900 MPa pressure, is 3 orders of magnitude greater than that of hot-pressed Bi2S3. Its highest ZT at 325 K of 0.006 is over twice of that of similarly prepared CuS or Ag2S-based nanocomposites. A significantly improved TE performance potential near 300 K is demonstrated for these toxic-free and rare-earth element-free TE nanocomposites, making the present synthesis method as a pioneering approach for developing enhanced thermoelectric properties of Bi2S3-based materials without extra sintering steps.

Structural correlations in the enhancement of ferroelectric property of Sr doped BaTiO3.

The effect of Sr doping in BaTiO3 (BTO) with nominal compositions Ba0.80Sr0.20TiO3 (BSTO) have been explored on its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K, which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (P r) of BSTO is much higher than in BTO. The value of P r is ∼5 µC cm-2 at room temperature and the maximum P r ∼ 8 µC cm-2 is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature ΔT ∼ 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron x-ray diffraction and Raman results show correlations between P r, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed in correlations with the appearance of superlattice peak around room temperature due to TiO6 octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials.

Spin reorientation transition and coupled spin-lattice dynamics of Sm0.6Dy0.4FeO3.

In this work, we have presented a solid-solution of Sm0.6Dy0.4FeO3 in the form of nano-particles having spin reorientation transition (SRT) at a temperature interval of 220-260 K. The lattice dynamics of Sm0.6Dy0.4FeO3 have investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. A negative thermal expansion at low temperatures has observed, which might be due to the interaction between Sm3+ and Fe3+ sublattice. Anomalous behavior in lattice parameters, octahedral tilt angle, and bond lengths have observed in the vicinity of SRT, which confirms the existence of magneto-elastic coupling in the system. The strong anomaly has observed in linewidth and phonon frequencies of Raman modes around SRT, which may be related to the spin-phonon coupling in Sm0.6Dy0.4FeO3. The contribution of SRT in lattice change and the presence of spin-phonon coupling can help to understand the correlation between the magnetic and structural properties of orthoferrite.

Spin phonon coupling in Mn doped HoFeO3 compounds exhibiting spin reorientation behaviour.

An investigation has been carried out on the spin phonon coupling in a series of isostructural polycrystalline orthorhombic (Space group Pnma) compounds HoFe1-X Mn X O3 (x ⩽ 0.6) exhibiting spin reorientation below Néel temperature (T N), using magnetization, neutron diffraction, and Raman scattering techniques. Mn doping leads to an anomalous increase in the spin reorientation temperature (T SR), shifting it close to room temperature from T SR ~ 60 K for x = 0 sample, and concomitant lowering of T N. The T SR is absent in samples for x ⩾ 0.5. The magnetic structure undergoes a transition at T SR from Γ4 → Γ1 in the Mn doped compounds as against Γ4 → Γ2 observed in HoFeO3 sample. In the region T < T N an anomalous softening of Raman phonon modes viz., B 2g(5) and B 3g(3), identified with the stretching motion and breathing mode, respectively, of Fe/Mn-O6 octahedra, is observed in compounds exhibiting spin-reorientation behaviour, indicating a spin-phonon coupling in these compounds. A quadratic correlation between the deviation of phonon frequency and variation of antiferromagnetic moment (Δω [Formula: see text] M 2) is observed in these compounds. The temperature evolution of the M2+ mode obtained from the analysis of neutron diffraction data based on symmetry adapted mode decomposition of the Pnma structure further corroborates the mode softening observation.

Porous and highly conducting cathode material PrBaCo2O6-δ: bulk and surface studies of synthesis anomalies.

The paradigm that chemical synthesis reduces the sintering temperature as compared to solid state synthesis seems to be violated in the case of the PrBaCo2O6-δ double perovskite. The sintering temperatures for pure phase samples synthesized through the solid state route (P-SSR) and the auto-combustion route (P-ACR) were found to be 1050 and 1150 °C, respectively. The porous microstructure of P-SSR is suitable for SOFC cathode materials while that of P-ACR is pore free. High-resolution transmission electron microscopy, Raman and scanning tunneling microscopy studies reveal that there is crystal growth on a smooth surface with a preferred orientation. Our results show that this anomalous synthesis behaviour is due to anisotropic surface nucleation growth. Thermodynamically, the higher decomposition temperature in the chemical route is due to stronger electron-phonon coupling and the higher value of change in entropy. The variation in the Co-O-Co bond angle reveals Jahn-Teller vibrational anisotropy in the-b plane leading to the anisotropic synthesis behaviour. This anisotropy is the reason for the violation of the paradigm.

Spontaneous Reduction of Copper(II) to Copper(I) at Solid-Liquid Interface.

Oxidation and reduction reactions are of central importance in chemistry as well as vital to the basic functions of life and such chemical processes are generally brought about by oxidizing and reducing agents, respectively. Herein, we report the discovery of an interfacial reduction reaction (IRR) - without the use of any external reducing agent. In course of metal-ligand coordination, spontaneous reduction of Cu(II) to Cu(I) at a solid-liquid interface was observed-unlike in a liquid-phase reaction where no reduction of Cu(II) to Cu(I) was occurred. High-quality thin films of a new coordination network compound bearing a Fe(II)-CN-Cu(I) link were fabricated by IRR and employed for efficient electro-catalysis in the form of oxygen reduction reaction. Also, thermally activated reversible structural phase transition modulated the electron transport property in thin film. This work unveils the importance of chemical reactions at solid-liquid interfaces that can lead to the development of new functional thin film materials.

Correlation between piezoelectric and magnetic properties of Fe and Sm co-substituted potassium niobate piezoelectric ceramics.

A piezoelectric material KNbO3 has been co-substituted with the magnetic ions Sm3+ and Fe3+ in order to explore the relation between piezoelectricity and magnetism. The samples K1-xSmxNb1-xFexO3 [x = 0.0-0.1] were synthesized using a solid state reaction route, after estimating the structural stability with the substitution. Structural studies were employed using XRD with Rietveld refinement and Raman analysis suggesting Amm2 symmetry. Also, the transition temperature was observed to change with the increase in Sm and Fe content. This transition temperature was also confirmed through high temperature XRD and high temperature Raman results. The dielectric and piezoelectric properties were found to be in correlation with the intensity of Raman modes for substituted samples, indicating better ferroelectricity at x = 0.05. A correlation between piezoelectric and magnetic properties was established in terms of the coercive field and exchange energy.

Competition and coexistence of polar and non-polar states in Sr1-x Ca x TiO3: an investigation using pressure dependent Raman spectroscopy.

The competition and cooperation between ferroelectric and anti-ferro-distortion (AFD) instabilities are studied using pressure dependent Raman spectroscopy on polycrystalline powder samples of Sr1-x Ca x TiO3(x = 0.0, 0.06, 0.25, 0.35). For x = 0.0 composition, a broad polar mode is detected in the Raman spectra above 6 GPa, while for x = 0.06 composition, the polar modes appear well above 9 GPa where the AFD modes showed strong suppression. In x = 0.25 and 0.35 composition, the application of small pressure resulted in the appearance of strong AFD modes suppressing the polar modes. At elevated pressures, re-entrant polar modes are observed along with the broad AFD modes and some new peaks are also observed, signifying the lowering of local symmetry. The reappearance of polar modes is found to be related to pressure induced symmetry disorder at local level, suggesting its electronic origin. The re-entrant polar modes observed at higher pressure values are found to be significantly broad and asymmetric in nature, signifying the development of ferroelectric micro regions/nano domains coexisting with AFD. The lower symmetry at local length scale provides a conducive atmosphere for coexisting AFD and FE instabilities.

Vibrational and electronic spectroscopic studies of melatonin.

We report the infrared absorption and Raman spectra of melatonin recorded with 488 and 632.8 nm excitations in 3600-2700 and 1700-70 cm(-1) regions. Further, we optimized molecular structure of the three conformers of melatonin within density functional theory calculations. Vibrational frequencies of all three conformers have also been calculated. Observed vibrational bands have been assigned to different vibrational motions of the molecules on the basis of potential energy distribution calculations and calculated vibrational frequencies. Observed band positions match well with the calculated values after scaling except NH stretching mode frequencies. It is found that the observed and calculated frequencies mismatch of NH stretching is due to intermolecular interactions between melatonin molecules.

Antimicrobial activity of silica coated silicon nano-tubes (SCSNT) and silica coated silicon nano-particles (SCSNP) synthesized by gas phase condensation.

Silica-coated, silicon nanotubes (SCSNTs) and silica-coated, silicon nanoparticles (SCSNPs) have been synthesized by catalyst-free single-step gas phase condensation using the arc plasma process. Transmission electron microscopy and scanning tunneling microscopy showed that SCSNTs exhibited a wall thickness of less than 1 nm, with an average diameter of 14 nm and a length of several 100 nm. Both nano-structures had a high specific surface area. The present study has demonstrated cheaper, resistance-free and effective antibacterial activity in silica-coated silicon nano-structures, each for two Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) was estimated, using the optical densitometric technique, and by determining colony-forming units. The MIC was found to range in the order of micrograms, which is comparable to the reported MIC of metal oxides for these bacteria. SCSNTs were found to be more effective in limiting the growth of multidrug-resistant Staphylococcus aureus over SCSNPs at 10 µg/ml (IC 50 = 100 µg/ml).

Dielectric, structural and Raman studies on (Na(0.5)Bi(0.5)TiO(3))((1 - x))(BiCrO(3))(x) ceramic.

Dielectric, structural and Raman investigations were carried out on a perovskite-based solid solution of (NBT)((1 - x))(BiCrO(3))(x) (x = 0.00, 0.05, 0.10 and 0.15). The crystal structure is rhombohedral, R3c, for these compositions and the anti-phase (a( - ) a( - ) a( - )) tilt angle decreases with increasing BiCrO(3) content. The temperature and frequency dependent dielectric measurements show that the phase transition temperatures T(d) and T(R - T) decrease, while T(m) increases, almost linearly with an increase in BiCrO(3) content. An anomalous increase in the relative dielectric permittivity is observed at higher temperature (T > T(d)) and higher BiCrO(3) content. However, at lower temperature (T < T(d)) the dielectric permittivity decreases with an increase in BiCrO(3) content. These effects are explained on the basis of the dynamics of oxygen defects produced due to charge compensation. The defect related bands are observed in the Raman spectra of (NBT)((1 - x))(BiCrO(3))(x).

High coercivity of oleic acid capped CoFe2O4 nanoparticles at room temperature.

High coercivity (9.47 kOe) has been obtained for oleic acid capped chemically synthesized CoFe(2)O(4) nanoparticles of crystallite size approximately 20 nm. X-ray diffraction analysis confirms the formation of spinel phase in these nanoparticles. Thermal annealing at various temperatures increases the particle size and ultimately shows bulk like properties at particle size approximately 56 nm. The nature of bonding of oleic acid with CoFe(2)O(4) nanoparticles and amount of oleic acid in the sample is determined by Fourier transform infrared spectroscopy and thermogrvimetric analysis, respectively. The Raman analysis suggests that the samples are under strain due to capping molecules. Cation distribution in the sample is studied using Mossbauer spectroscopy. Oleic acid concentration dependent studies show that the amount of capping molecules plays an important role in achieving such a high coercivity. On the basis of above observations, it has been proposed that very high coercivity (9.47 kOe) is the result of the magnetic anisotropy, strain, and disorder of the surface spins developed by covalently bonded oleic acid to the surface of CoFe(2)O(4) nanoparticles.

Study of swift heavy-ion-induced modification in Ti/Si using x-ray standing waves.

Intermixing in a Si/Ti/Si tri-layer induced by 120 MeV Au ions has been studied. X-ray standing wave analysis combined with x-ray reflectivity has been used to get a depth profile of the Ti marker layer with an accuracy of a fraction of a nanometer. Two different thicknesses of the Ti marker layer have been used to study the possible effect of layer thickness on intermixing. In the case of a 2 nm thick Ti layer intermixing is stronger as compared to a 6 nm Ti film, which can be understood in terms of a stronger confinement of the dissipated energy in the Ti layer due to increased interface scattering of δ-electrons in the case of the 2 nm thick Ti layer. In the 6 nm thick Ti layer, intermixing is asymmetric at the two interfaces, which may be due to a possible asymmetry in the interface structure in the as-deposited film itself.