Temperature Dependence Of Relaxation Research Articles

First-principles and experimental study of structural, electronic, and enhanced dielectric response in Bi2Ca1.95Sm0.05CoO6 nanoparticles

In this study, we synthesized Bi2Ca1.95Sm0.05CoO6 (BCSCO) by the Co-precipitation route. X-ray diffraction was used for structural analysis, which confirmed the monoclinic structure with space group P21/m. Here, we employ the CASTEP (Cambridge Serial Total Energy Package) approach, we conducted a theoretical investigation of the structure, electronic, and optical properties of BCSCO double perovskites. FTIR spectra, BCSCO presents three absorption bands that correspond to the Bi(Ca)-O, O-Co-O, and Co-O. The morphological study showing the agglomeration phenomenon has occurred in the synthesized sample. The AC conductivity and dielectric response have also been studied as a function of frequency (100 Hz-3 MHz) at different temperatures (100 °C-600 °C). Temperature-dependent dielectric relaxation was investigated, and employing the non-linear Debye fitting to determine the spreading factor and relaxation time. The maximum value of the dielectric constant is 2.4 × 106 at 600 °C. AC conductivity is examined at (100 °C-600 °C) using Jonscher’s power law. The model fitting shows the Overlapping Large Polaron Tunneling conduction mechanism for BCSCO. In order to explore the impact of grain barriers and interior, the Nyquist plot was utilized, and the results are inter-connected.

Slow magnetic relaxation behaviors and diamagnetic dilution studies of a carboxyl bridged dinuclear dysprosium(III) complex

By using a rigid bulky carboxylic ligand α-cyanocinnamic acid (CCA), a dinuclear dysprosium (III) complex [Dy2(CCA)6 (MeOH)4] (1) was synthesized. Single crystal X-ray crystallography reveals that the two eight-coordinate dysprosium ions are bridged by four deprotonated carboxyl groups, forming a centrosymmetric paddle-wheel-like structure. Dynamic magnetic property measurements indicate that complex 1 displays field-induced slow magnetic relaxation. The temperature-dependent relaxation times can be fitted using Orbach and Raman processes with parameters of n = 2.8 (2), C = 27 (8) s−1/Kn, τ0 = 5 (2) × 10−10 s and Ueff = 40 (3) cm−1. Magnetic studies on the diamagnetic YIII-diluted analogue [Dy0.206Y1.794(CCA)6 (MeOH)4] (2) reveal its slow magnetic relaxation behavior without external dc field and the antiferromagnetic coupling between the DyIII ions in 1. Fits on the obtained relaxation times of 2 lead to the parameters of n = 4.5 (3), C = 0.7 (2) s−1/Kn, τ0 = 2.8 (2) × 10−9 s and Ueff = 38 (2) cm−1. The results suggest that slow magnetic relaxation originates from the single-ion relaxation of DyIII ions. Moreover, the diamagnetic dilution can suppress other fast relaxation pathways at low temperature, on account of the elimination of magnetic coupling and dipolar interaction. Ab initio calculations were then performed on the single DyIII ion species {YDy} and indicate that the first excited Kramers doublets (KDs) lie at ca. 76 cm−1, which is slightly higher than the experimental Ueff value. The intramolecular magnetic interactions were also calculated and indicate a weak ferromagnetic dipole-diploe magnetic interaction and an antiferromagnetic exchange coupling.

Structural, electrical and dielectric properties of ZnFe2O4/Cu2S 3D heterostructures

This work reports the fabrication of zinc ferrite-copper sulphide (ZnFe2O4/Cu2S) 3D heterostructures and subsequent investigation of the spectroscopic behaviour of various electrical parameters like conductivity, impedance and dielectric loss. The study reveals a non-monotonic behaviour of the real component of impedance (Z’), while the imaginary component of impedance (Z’) exhibits a temperature-dependent relaxation frequency, with an estimated activation energy (E a ) of 220.13 meV. The dc conductivity (σ dc ) measurements reveal the semiconducting nature of the sample and a transition from a ferrimagnetic to a paramagnetic behaviour is reported at the Curie temperature of 327 K. In case of ac conductivity (σ ac ), Jonscher’s power law σ ac = Aω n is followed and the exponent n is found to lie in the range 0.679–0.735 at different temperatures, which is best fitted into a polynomial of degree six. The temperature variation of n is suggestive of the overlapping large polaron tunnelling (OLPT) model. Further, ac activation energy (E ac ) is also calculated, which is found to be smaller than the dc activation energy (E dc ), indicating electron hopping between Fe3+ and Fe2+ ions. The numerically computed staying time (τ) of electrons in Fe3+/Fe2+ ionic sites varies with frequency as well as with temperature, ranging from 10−6s to 10−19s. A significant decrease in dielectric loss (tanδ) to the tune of 99% (from 75 at ∼100 Hz to 0.89 at ∼1 MHz) is reported at room temperature. In the present scenario, when smart materials like spinel ferrites have garnered significant attention for their promising magnetic and electric properties, our studies of the ZnFe2O4/Cu2S 3D heterostructures may provide immense possibilities for tailored applications in various electromagnetic applications.

Extending the Experimentally Accessible Range of Spin Dipole-Dipole Spectral Densities for Protein-Cosolute Interactions by Temperature-Dependent Solvent Paramagnetic Relaxation Enhancement Measurements.

Longitudinal (Γ1) and transverse (Γ2) solvent paramagnetic relaxation enhancement (sPRE) yields field-dependent information in the form of spectral densities that provides unique information related to cosolute-protein interactions and electrostatics. A typical protein sPRE data set can only sample a few points on the spectral density curve, J(ω), within a narrow frequency window (500 MHz to ∼1 GHz). However, complex interactions and dynamics of paramagnetic cosolutes around a protein make it difficult to directly interpret the few experimentally accessible points of J(ω). In this paper, we show that it is possible to significantly extend the experimentally accessible frequency range (corresponding to a range from ∼270 MHz to 1.8 GHz) by acquiring a series of sPRE experiments at different temperatures. This approach is based on the scaling property of J(ω) originally proposed by Melchior and Fries for small molecules. Here, we demonstrate that the same scaling property also holds for geometrically far more complex systems such as proteins. Using the extended spectral densities derived from the scaling property as the reference dataset, we demonstrate that our previous approach that makes use of a non-Lorentzian Ansatz spectral density function to fit only J(0) and one to two J(ω) points allows one to obtain accurate values for the concentration-normalized equilibrium average of the electron-proton interspin separation ⟨r-6⟩norm and the correlation time τC, which provide quantitative information on the energetics and timescale, respectively, of local cosolute-protein interactions. We also show that effective near-surface potentials, ϕENS, obtained from ⟨r-6⟩norm provide a reliable and quantitative measure of intermolecular interactions including electrostatics, while ϕENS values obtained from only Γ1 or Γ2 sPRE rates can have significant artifacts as a consequence of potential variations and changes in the diffusive properties of the cosolute around the protein surface. Finally, we discuss the experimental feasibility and limitations of extracting the high-frequency limit of J(ω) that is related to ⟨r-8⟩norm and report on the extremely local intermolecular potential.

Desolvation-induced magnetic switching from single-ion magnetism to spin-crossover in a halogen-functionalized cobalt(II) complex

The switching between spin-crossover (SCO) and single-ion magnet (SIM) are fascinating because the process provides potential in-depth understating of different bistability. Herein, we present a rare example of the desolvation-induced magnetic switching from single-ion magnetism to SCO between a halogen-functionalized cobalt(II) complex, [Co(Brphtpy)2](PF6)2·2MeOH (Brphtpy = 4′-(4-Bromophenyl)-2,2′:6′,2′'-terpyridine, 1·2MeOH) and its desolvated material of [Co(Brphtpy)2](PF6)2 (1). The temperature-dependent magnetic susceptibility and variable-temperature single crystal X-ray diffraction results show a high spin state of the Co(II) ions in 1·2MeOH. At lower temperature, frequency- and temperature-dependent slow magnetic relaxation behaviors were evidenced under an applied dc field of 1000Oe, originating from the easy-plane magnetic anisotropy (D=43.5 cm−1) of Co(II) ions. After the release of methanol molecules, interestingly, the desovated material 1 display a complete and cooperative two-step spin transitions with transition temperatures being 350 and 125K. Differential scanning calorimetry measurements support the stepwise SCO behavior and reveal the related ΔH and ΔS.

Temperature dependent dielectric relaxation spectroscopy of amyl acetate-xylene solutions – An approach to molecular and co-operative dynamics

Dielectric relaxation parameters of AMA-Xylene solutions have been investigated thoroughly to discern the associativeness as well as heterogeneous behavior among the hetero molecules in the solutions such that dielectric constant (εo) and relaxation time (τ) of solutions has been determined. Complex permittivity spectra (CPS) for Amyl Acetate (AMA)-Xylene solutions were measured in 10 MHz–50 GHz frequency range using Time domain reflectometry (TDR) technique. It is exciting to explore the cooperative nature and association between AMA-Xylene. With co-operative domains (CDs), dynamics in AMA-AMA and AMA-Xylene molecules have been explicated while Kirkwood validates CDs with diverse exchanges through bonding. The experimental values of εo are compared with theoretical values obtained from the molecular parameters suggested by the Luzar. Thermodynamic parameters for AMA-Xylene show positive values of Enthalpy and Entropy for all concentrations, indicating that the system is endothermic and less ordered. Gibbs free energy decreases with increase in volume fraction of amyl acetate (VAMA).

Optoelectronic and thermoelectric properties of LiCuM (M=S, Se and Te) half-Heuslers: insights first principle calculations

The work is performed to study the structural stability and optoelectronic properties as well as thermoelectric properties of LiCuM (M=S, Se and Te) half-Heusler semiconductors using density functional theory (DFT) and semi-classical Boltzmann transport. The ground state results show that the compounds exhibit semiconducting behavior with a direct band-gap. The elastic parameters indicate that the present compounds are mechanically, dynamically stable and brittle. The calculated optical properties in GGA and GGA+U approaches show that the dominant response in the low ultraviolet and visible energy regions. The thermoelectric properties are evaluated using the Slack model and temperature dependent relaxation time in the temperature range of 100 K to 1000 K. The response of thermoelectric properties to temperature is evaluated and discussed in detail. The figure of merit with relaxation time is found to increase with temperature and reaches the optimal values in GGA and GGA+U at 1000 K are 0.69(0.01), 0.66(0.665) and 0.67(0.778) for LiCuS, LiCuSe and LiCuTe, respectively. The lattice thermal conductivity decreases with increasing temperature. These properties make these compounds promising candidates for optoelectronic and thermoelectric devices.

Microstructure correlated optical, electrical, mechanical properties and photodegradation activities of mechanically alloyed nanocrystalline Bi1.5Sb0.5Te3 as a thermoelectric material and efficient photocatalyst

Phase pure and 25 % Sb incorporated Bi2Te3 compounds with a rhombohedral crystal structure are synthesized by mechanical alloying the stoichiometric mixtures of elemental powders within 3 h under an inert atmosphere. The structure and microstructure of the synthesized samples are revealed by analyzing XRD patterns with Rietveld refinement, FESEM, HRTEM images, and EDX spectra. The increment of lattice parameter ‘c’ with increasing milling time is associated with the increased [Bi/SbTe] type antisite defects. Optical bandgaps of the pure and Sb-alloyed Bi2Te3 samples of different sizes are determined from the FTIR spectra. The transition of undoped n-type to Sb-alloyed p-type semiconducting nature is revealed from the photo responses of the samples. The ac electrical conductivity as well as complex impedance spectra in the temperature range 303–403 K reveal the semi-metallic, non-Debye type behavior of the samples and temperature-dependent relaxation phenomena. The change in electrical conductivity and the corresponding activation energies due to Sb alloying and for different grain sizes are explained in terms of antisite defects and porosity of materials. The temperature variation of the frequency exponent has been demonstrated with the small polaron hopping transaction. The Mott VRH model is used to explain the electrical conduction mechanism of the synthesized samples. The variation of Vickers microhardness with the grain size of milled samples corroborates well with the Hall-Petch relation. The normal indentation size effect (ISE) is depicted from Meyer's law. The photocatalytic activity of 10 h milled Sb-alloyed sample to degrade Rhodamine B cationic dye in wastewater is ∼ 91 %. The correlations of electrical and mechanical properties with the photocatalytic activity of the samples have been established.

Low-frequency electrical response related to oxygen vacancies in Al3+ substituted M-type hexaferrite

The presence of oxygen vacancies is unavoidable in many complex metal oxide materials such as hexaferrites. This article investigates the role of crystal defects, such as oxygen vacancies, and different oxidation states of Fe ions, on the electrical conduction behaviors of Al3+ substituted Ba0.4La0.1Sr0.5Al x Fe12−x O19 hexaferrites by analyzing the temperature dependent AC impedance and AC conductivity. The optimal substitution of La3+ ions and high-temperature sintering is responsible for forming oxygen vacancies while reducing Fe from Fe3+ to Fe2+ cations, as observed in structural and XPS analysis, which affects electrical conduction behaviors. The departure from ideal Debye-type relaxation behavior is also one of the effects of crystal defects. Temperature variation of relaxation time shows a sharp change at around 403 K. This may be due to different electrical entities influencing the mode of electron hopping with temperature. The activation energy calculated from the temperature dependent relaxation time confirmed the presence of electron hopping through the bridging effects of the first ionization of oxygen vacancies Fe2+––Fe3+ below a temperature of 403 K. Above 403 K, electron hopping through different oxidation states of Fe3+ + e− → Fe2+ and migration of oxygen vacancies toward the bulk surface are responsible for the conduction mechanism. The DC resistivity and AC conductivity show that the bridging effects of oxygen defects can also induce Coulomb interaction between the defect sites resulting in Efros–Shklovskii variable range hopping and correlation barrier hopping below 403 K. Above 403 K, polaron-assisted electron hopping is more desirable, as confirmed by the non-overlapping small polaron tunneling model.

Disorder induced cluster spin glass like state in MnFeSb

Hexagonal MnSb is a ferromagnet with Curie temperature and saturation magnetization values of 587 K and 110 emu/g, respectively. In this paper, the origin of the complex magnetic behavior of a single phase MnFe0.20Sb prepared using solid-state reaction method is examined. A thorough investigation of temperature dependent magnetization and magnetic relaxation measurements reveals the presence of a glassy like phase below 15 K. AC susceptibility measurements revealed the existence of a cluster glass-like state with a freezing temperature of 18 K. The presence of competing magnetic interactions and random occupation of Fe atoms at 2d site leads the system to exhibit a cluster glass state. Furthermore, resistivity measurements indicate that the material exhibits a Kondo-like behavior below 30 K and can be attributed to the interaction of conduction electrons with localized Mn moments.

Dynamic memory tuned by frequency in a homologous thermotropic liquid crystal.

With scaling of dynamic RAM and NAND memory technologies reaching a limit, there is a need for dynamic memory with high density. In this work, an investigation on existence of dynamic memory feature in a frequency tuned homologous series of thermotropic liquid crystals has been carried out. A homologues series of five thermotropic liquid crystalline compounds comprising of 4-butyl benzoic acid and various alkyloxy benzoic acids are prepared, and all these mesogens exhibit only nematic phase. Liquid crystal dynamic memory storage setup consists of a conducting transparent glass cell with two indium tin oxide coated transparent glass plates acting as electrical electrodes in which the selected thermotropic liquid crystal is filled by capillary action. The temperature dependent dielectric relaxation studies enable to elucidate the relaxation frequency of each of these mesogens in nematic phase. The liquid crystal at different temperatures is excited with the relaxation frequency at various chosen fields, and the dielectric hysteresis is recorded. The magnitude of the hysteresis loop is directly proportional to the memory storage capacity. The main objective of this work is observation of dynamic memory storage in liquid crystals exhibiting nematic phase, at different frequencies in a thermotropic liquid crystal as the ingredient in a conducting polyamide buffed glass cell excited by an external electrical dc stimulus. The variation of the hysteresis loop with varying field; temperature and frequency are also studied and reported in this work.

Investigation on structural, optical and electrical properties of BiFeO3:ZnO nano–micro particles–matrix composite

A new class of materials called matrix-nano composites has the ability to meet the needs of modern advanced applications and technology. To prepare the BiFeO3:ZnO composite, BiFeO3 nanoparticles were prepared using a low–cost sol–gel method, to which ZnO in its micron-sized form was added in varying concentrations of 5%, 10%, and 15%. The structural, morphological, and optical properties of the pure and composite materials were characterized using XRD, FESEM, EDAX, PL spectra, and UV-Visible spectroscopy. The dielectric properties of the pristine and composites were investigated at room temperature. The a.c. conductivity fit with Jonscher's power law and CBH model described the charge conduction behaviour in all pure and composite materials. The temperature-dependent dielectric and loss measurements showed a temperature dependent relaxation process. UV–vis and PL characterization show that the composite materials exhibited improved charge separation efficiency and wider band gaps with increasing BFO content.

The Nature of the Low-Temperature Crossover of Water in Hard Confinement.

The dynamics of water confined in mesoporous MIP (2-3 nm pores in size) with silica gel (secondary silica; further, the abbreviation SG will be used) and MAP (10-35 nm pores in size) without SG borosilicate glasses have been studied by broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). MIP samples contain secondary silica inside the pores and provide a confinement size of about 2-3 nm, whereas MAP samples are free of secondary silica and provide a confinement size of about 10-35 nm. It is shown by BDS and NMR techniques that water exhibits a dynamic crossover of around 180 K when it is confined in MIP samples. By contrast, water confined in larger pores (MAP) does not exhibit any changes in its relaxation behavior. It is also shown that the crossover temperature depends on the hydration level (the higher the hydration level, the lower the crossover temperature). Below the crossover temperature, we find that water reorientation is isotropic (NMR) and that the temperature-dependent dielectric relaxation strength (BDS) follows the tendency expected for a solid-like material. In contrast, water reorientation is related to long-range diffusion above the crossover temperature, and the dielectric relaxation strength follows the tendency expected for a liquid-like material. Furthermore, the calorimetric results are compatible with crossing a glass transition near 180 K. Finally, the results are discussed within the Gibbs-Thomson model. In this framework, the crossover could be related to ice crystals melting.

Small polaron hopping transport mechanism, dielectric relaxation and electrical conduction in NiAl2O4 electro-ceramic spinel oxide

In this study, the frequency and temperature dependent dielectric relaxation and electrical conduction mechanisms in NiAl2O4 spinel oxide ceramic have been explored in a frequency range of over a measured temperature from 163–283 K. The polycrystalline NiAl2O4 was synthesized via solid state reaction route and sintered at 1000 °C. The room temperature x-ray powder diffraction pattern confirmed the formation of NiAl2O4 spinel phase with Fd3m space group. The surface morphology of the sample was investigated by scanning electron microscopy and chemical properties by Fourier transform infrared spectroscopic analysis. Complex impedance studies revealed the presence of relaxation time distribution and charge carriers were found to be thermally activated. The Nyquist plots exhibited depressed semicircles and their fitting by an equivalent circuit model with configuration (RGCG)(RGBCGB) resolved the contributions of grains and grain-boundaries to the electrical transport properties of the material. Electrical conductivity analysis followed the Jonscher’s power law behavior and the frequency exponent suggested small polaron hopping as the governing transport mechanism in NiAl2O4 spinel oxide. Non-Debye type nature of dielectric relaxation was confirmed by the complex modulus analysis whereas dielectric constant and tangent loss analysis verified that the hopping mechanism was thermally activated.

Chemically ordered structure and dynamics in Al80Ti20 liquids

We conducted ab initio molecular dynamics simulations to study the structural and dynamical properties in Al80Ti20 liquids. The prepeak that represents some chemically ordered structure, emerges in the partial static structure factors at low temperatures. By calculating coordination numbers, we found a preferred connection for Al–Ti pairs, which induces an excess Ti/Al concentration around the central Al/Ti atoms. An excess Ti concentration is even found in the second neighbour shells around Ti atoms, rationalizing the prepeak as the result of chemical concentration fluctuation in these neighbour shells. Concomitantly, slow structural relaxation occurs below 1400K, exhibited as the second step relaxation in self-intermediate scattering function. The slow dynamics induces a non-Arrhenius transition for the temperature-dependent diffusivity and structural relaxation time, as well as the breakdown of the Stokes–Einstein relation. These results unveil the detailed ordering structure for the chemical interaction and the associated dynamical behaviour in Al80Ti20 liquids.

Formation of silver particles in [PVA:CS:PEG]-AgNO3 based biopolymer electrolyte membranes: Structural and electric transport properties study

[Chitosan (CS)-poly(vinyl) alcohol (PVA)-polyethylene glycol (PEG-200)]+xwt% silver nitrate (AgNO3) (x = 0, 10, 20, 30, 40) based biopolymer blend electrolytes (BPBEs) were prepared using solution casting method. FTIR results show the interaction of Ag+/NO3− with the constituents of polymers CS/PVA. XRD results reveal that the amorphousness increases with increasing AgNO3 concentration. Optical morphological (OM) images show that the silver, Ag(o) particles are agglomerated on the surface of the membrane. Temperature dependent dc conductivity (σdc) and dielectric relaxation frequency (fr) for BPBEs follow the Arrhenius type behavior and the sample containing 30 wt% salt has optimum dc conductivity, σdc∼1.7×10−4 S/cm at 30oC with lowest activation energy∼ 0.16 eV. The ac conductivity spectra follow the Jonscher's power law (JPL) with power law exponent, s > 1. The scaling of AC conductivity and loss tangent (tanδ) spectra were performed with respect to temperatures/concentrations of salt. The dielectric permittivity study reveals that the electrode polarization effect predominates at low frequencies. The Ionic Transference Number (ITN) measurement was used to determine the nature species of charge carrier, either ionic or electronic. The linear sweep voltammetry (LSV), result shows that 30% AgNO3containing sample has the electrochemical stability window (ESW) ∼+1.5 to -1.5 V.

Study of dielectric, impedance and transport properties of co-doped Ba0.5Sr0.5TiO3 ceramics

Dielectric properties and Electrical response of BST ceramics having composition Ba0.5Sr0.5Ti0.98Sn0.01Zr0.01O3 synthesized by solid state reaction route are studied in this piece of work. The structural part analysis is done using XRD technique and scanning electron microscopy and is confirmed to be of cubic structure. Electrical characterization through impedance and modulus spectroscopy is made over a frequency region of 1 kHz to 1 MHz from ambient temperature to 400 °C. Near constant value of Ɛr and significantly low and flat loss tangent at room temperature are achieved in the material which suggest possible application in electronic circuits. Temperature dependent broadened loss peaks observed beyond 250 °C indicated thermally activated conductivity/ relaxation process in the material. Impedance spectroscopy results were examined in alternate formalism for the role of grain boundary and grain in various processes. The computed activation energy for charge carriers provides information of the transport phenomena. The estimated values suggest that oxygen vacancies play important role in conduction process. The activation energy is estimated by fitting temperature dependent relaxation time with Arrhenius equation and the type of charge carriers involved in the relaxation process are suggested. Frequency dependent ac conductivity plots at various temperatures obey Johnscher’s law. Variation of exponent in Johnsher’s power law with temperature well agrees with correlated barrier hopping (CBH) model for ac conduction mechanism.

Structural study and temperature dependent relaxation and conduction mechanism of orthorhombic tungsten bronze Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic

In this study, the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic was prepared using the solid-state technique. The X-ray diffraction technique was used in this study to investigate the Ba/La order in the solid solution Ba4La28/3(Zr0.05Ti0.95)18O54. We have developed a structural model, to represent the order within the structure. The formula of model [Ba4−a□a]A2[La8+2b3□2−2b3]A1,A1′(Zr0.05Ti0.95)18O54 is described as perovskite layers with a thickness of 3 octahedral parallel to the xOz plane. Scanning electron microscopy (SEM) showed that Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic exhibits a typical columnar grain with a heterogeneous distribution over the entire surface. Complex impedance spectroscopy was used to analyze the dielectric and electrical properties of Ba4La28/3(Zr0.05Ti0.95)18O54 materials over a frequency range of 10 Hz to 1 MHz and a temperature range of 350°C to 400°C. An appropriate equivalent electrical circuit was also used to investigate the contributions of grains and grain boundaries. The AC-conductivity data was analyzed using Jonscher's universal power law. The thermal behavior of the exponent parameter "s" indicates that the dominant conduction mechanism in our compound is the non-overlapping small polaron tunneling (NSPT) model. The activation energies calculated from the conduction and relaxation mechanisms are nearly identical for the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic.

Investigations of structural, optical, dielectric and antimicrobial properties of Zirconia-Vanadia nanocomposite

Zirconia-Vanadia nanocomposite synthesized by coprecipitation-calcination technique was prepared. XRD plots confirmed the presence of both materials in the composite. SEM and TEM pictures showed the formation of spherical and needle shaped structures. EDX spectrum confirms the presence of both elements. A.C conductivity plots show a linear variation with frequency. Impedance analysis suggested a decrease in impedance with increase in temperature. Modulus analysis showed a temperature dependent relaxation process. The material has a high dielectric constant of about 2500, making it suitable for use as a gate dielectric. Antimicrobial activity analysis suggested the efficacy of the composite against three types of bacteria.

Unconventional floppy network structures in titanate glasses

Annealed titanate glasses are important candidate materials for high-performance electronic components, but their structural response to temperature-induced properties upon thermal annealing remains elusive. Here, using high-energy synchrotron X-ray scattering, high-temperature Raman spectroscopy, and empirical potential structure refinement simulation, we track the structural evolution in situ of a barium dititanate (BaTi2O5) glass upon annealing around and below the glass transition temperature. We find that the network structure is intrinsically floppy, as the network units ([TiOm] polyhedra) themselves and their topological packing can be easily modulated by annealing temperature. The floppy nature of the glassy titanate network challenges the currently well-cognized Rigid-Unit Mode model explaining temperature-driven structural reorganization of prototypical network glasses (e.g., silicate/borate glasses). As temperature increases, the floppy network of BaTi2O5 glass undergoes a non-monotonic, two-stage network rearrangement. After cooling back to room temperature, the distortion of network units is found recoverable whereas the change of network connectivity in the intermedium-range order is irreversible. Simulation ensembles further show the irreversible connectivity change can be ascribed to the local development of crystal-like cationic motifs, which in turn induce excess enthalpy relaxation. Our findings provide an atomic-scale perspective on temperature-dependent structural and enthalpy relaxation of a model titanate glass upon annealing, which are crucial for understanding thermal-related changes in the properties of titanate glasses.