Crystal Lattice Sites Research Articles

Effect of Varying Calcium Concentration on Dielectric Properties of Calcium Substituted Strontium M-Type Hexaferrites

Calcium substituted strontium M-Type hexaferrites are synthesized at different calcium concentrations by co-precipitation method. During synthesis process, PH value of 11 is achieved and solution is heated at 70 °C for 3 hours to form gel followed by drying process at 80 °C for 5 hours. Synthesized samples are then sintered at 650 °C for 4 hours at ramp rate of 10 °C/min. XRD analysis reveals that strontium M-Type hexaferrites at all calcium concentrations exhibit single phase hexagonal crystal structure. Change in density is observed for samples sintered at 800 °C as compared to samples sintered at 650 °C due to increase in temperature. SEM shows that the average particle size of strontium M-Type hexaferrites is greater at lower calcium concentration and smaller at higher concentrations. The average particle size varies from 530 nm to 345 nm for different calcium concentrations and fine particle sizes are achieved at all calcium concentrations. EDX results indicate that stoichiometric ratio is properly maintained according to samples composition and no extra peak of impurity or other element is detected in EDX spectrum. According to LCR measurement, pure strontium M-Type hexaferrites exhibit high dielectric constant at lower frequencies as compared to calcium substituted M-Type hexaferrites at different concentrations. Pure strontium M-Type hexaferrites have higher conductivity which might be due to presence of extra Fe3+ ions at crystal lattice sites. At lower frequencies pure strontium M-Type hexaferrites have higher conductivity and higher tangent loss at lower frequencies as compared to calcium substituted M-Type hexaferrites. While in the frequency range of 200 Hz to 300 Hz calcium substituted M-Type hexaferrites exhibit higher tangent loss.

Excess Energy Released Due To Proton-Proton Collisions in Condensed Matter Could Be Due To Laboratory-Made Micro Black Holes

While sodium metal dissolution in concentrated (2M) Epsom solution is very peaceful under stirring conditions in about 5 to 10s, its dissolution in a dilute (0.85) Epsom solution has turned very violent. Nearly 30s after the addition of Na, the solution exploded accompanied by the vaporization of the glass beaker. Only sodium aerosol and tiny molten needles of glass were seen around indicating a very high temperature (>1000 0C) has indeed been reached. The timing of the explosion has indicated that hydrogen released during sodium dissolution has got trapped in the salt solution and subsequent energy build-up has caused the excess energy release. A viable trapping mechanism involving the exchange of 2 hydrogen ions (H22+) with an Mg2+ ion in cavitation-induced nanocrystals of Epsom has been proposed in this regard. The two hydrogen ions are stabilized at the cation vacancy (cavity) by dative bonds with the two hydrogen ions in the water molecule trapped at a neighboring sulphate vacancy. Spring-like action between the two protons trapped at the cation vacancy due to oscillations caused by two opposing forces – one by cavitation and the other by coulombic repulsion eventually appear to have led to the collision of hydrogen ions at relativistic speeds in condensed matter. To start with, the two protons in the H22+ species are confined in a small space (72 pm cavity) at a single crystal cation lattice site in Na2SO4 nanocrystal which increases their head-on collision probability at high energies. There is no upper limit to the energies achieved through p-p collisions in this species as the Cavitation-Coulombic Repulsion Oscillations (CCRO) can continue until the endpoint is reached. Regeneration of a nanocrystal over a sufficiently small time scale and regeneration effect prior to cavitation collapse are all important so laws of thermodynamics are not violated. Extra dimensions of gravity at short distances, if present, could also assist in the high energies required for the production of mini black holes in condensed matter. Such black holes lose mass very quickly through the emission of Hawking radiation observed in the form of explosion with mass-energy equivalence of E = mc2. The possibility of tapping such explosive energy for peaceful purposes is discussed. As such it constitutes the third kind of atomic energy humans have entertained, the first two being fission and fusion.

Quantum features of low-energy photoluminescence of aluminum nitride films

Photoluminescence of aluminum nitride films at the below bandgap excitation has been studied. It has been found that low-energy (up to 2.02 eV) photoluminescence spectra of the AlN films contain a series of equidistant maxima, the intensities of which decrease with energy. Theoretical analysis has shown that the observed photoluminescence features may be caused by strong electron-phonon interaction (long-range interaction of electrons in the band gap with Al3+ ions in the lattice sites). This interaction presumably leads to appearance of quasi-particles in the band gap of AlN, which are a bound state of an electron with an ion in a crystal lattice site. Such quasi-particles have been called “elions”. The energy of an elion is quantized. An elion quantum is equal to the longitudinal optical phonon energy. The low-energy photoluminescence is based on the elion generation and subsequent annihilation mechanism.

A novel platinum modified barium zirconate-based electrolyte for enhanced solid oxide fuel cell performance

Pt modified BaZr0.76Y0.2Ni0.04O3 (BZYN) is fabricated and characterized as a stable electrolyte for proton-conducting solid oxide fuel cell (H-SOFC). The utilization of X-ray diffraction method (XRD) and transmission electron microscopy (TEM) enables the identification of the presence of platinum (Pt) in both the crystal lattice sites and the grain interface. This occurrence contributes to a reduction in grain boundary resistance. Consequently, this phenomenon improves the conductivity of the electrolyte. The electrochemical performance of the single cell with Pt-modified BZY electrolyte is improved by the reduction of ohmic resistance and enhancement of ion migration. This signifies a noteworthy advancement in the creation of more efficient and durable proton-conducting SOFCs.

Local symmetry of manganese ions in MgAl2O4 optical nanoceramics

Optically transparent nanoceramics of the composition Mg1-xMnxAl2O4(x = 0.005) with a grain size of 15–40 nm were obtained by thermobaric synthesis in a toroid-type high-pressure chamber in the range P = 4–9 GPa at a temperature of 600 °C. EPR spectroscopy indicates the presence of divalent manganese ions with a characteristic HFS signal. In addition, the signal from F+ centers were registered in the EPR spectrum. It has been established that in the HFS of impurity Mn2+ there is an additional contribution from manganese centers split in the field of rhombic symmetry. Photoluminescence spectroscopy methods revealed the presence of optically active centers based on Mn3+ and Mn4+. With an increase in the synthesis pressure, the conversion of manganese ions localized in octa- and tetra-positions occurs, accompanied by a change in valence. It has been found that some manganese ions with a valence of 2+ can be localized in an octahedral oxygen environment, occupying anti-site positions with reduced point symmetry. The formation of F-type centers, as well as polyvalent manganese centers, was confirmed by the cathodoluminescence method. Changing the synthesis parameters makes it possible to control the ratio of valence manganese ions in the corresponding sites of the spinel crystal lattice, thereby expanding the methodological base of defect nanoengineering.

A comparative study of the correlation among the phase formation, crystal stability and magnetic properties of SrFe12-xMxO19 (M=Al3+, Cr3+ and Mn3+, x=0–0.5) ferrite permanent magnets

The aim of this study is to enhance the magnetic and thermal properties of strontium hexaferrites by substituted with Al, Cr, and Mn ions instead of Fe, and to elucidate the changes in their structural, morphological, and thermal characteristics, in detail. SrFe12-xMxO19 (M: Al, Cr, Mn; x = 0.1, 0.3, and 0.5) powders were produced by the mechanochemical synthesis method from mill scale, which is a solid waste in steel production. While the Al3+ substitution did not cause any change in the phase structure, the Cr3+ and Mn3+ caused the formation of nanosized α-Fe2O3 and MnδFe2-δO4 phases in the structure, respectively. Increasing the Al substitution ratio led to a decrease in crystal size, from 176 nm to 32 nm. Similarly, the substitution of Cr resulted in a decrease in crystal size to 78 nm. However, Mn substitution had the opposite effect, increasing the crystal size of the powders. Al3+, Cr3+, and Mn3+ substitutions led to various effects on magnetic properties due to their placement in different lattice sites in the SrFe12O19 hexagonal crystal. The residual or remanent magnetization (Mr) and saturation magnetization (Ms) were lower than the initial values of Mr = 41.76 and Ms = 69.94 emu/g depending on the type and ratio of substitution ions. The highest coercivity was observed as 7116 Oe for SrFe11.5Al0.5O19. The Curie temperature increased to 515 °C with Cr3+ substitution but decreased to 431 °C and 426 °C with Al3+ and Mn3+, respectively.

Facile synthesis, novel structure, multicolor luminescence, and potential applications of lanthanide ions doped bismuth titanate phosphors

A variety of lanthanide ions doped bismuth titanate (Bi4Ti3O12) luminescent materials with eminent down-conversion (DC) and up-conversion (UC) luminescence performance have been fabricated via a facile sol-gel approach. The XRD, XPS, and EDX elemental mapping results confirm the phase structure of orthorhombic Bi4Ti3O12 (BTO), and the lanthanide activator ions occupy the Bi3+ lattice sites in the BTO crystal. Under UV or NIR excitation, the Eu3+, Yb3+/Ln3+ (Ln = Er, Tm, and Ho) doped Bi4Ti3O12 samples exhibit characteristic red, green, blue, and green emissions. The luminescent mechanisms of the BTO:Eu3+ and BTO:Yb3+/Ln3+ samples are discussed based on the energy level diagrams. The doping concentrations of Eu3+, Yb3+, Er3+, Tm3+, Ho3+ ions and annealing temperature and time are optimized, whose optimal values are determined to be 14, 8, 1, 0.4, 1 mol% and 800 oC, 4 h. The as-obtained LED devices fabricated by Bi4Ti3O12:Eu3+ and Yb3+/Ln3+ phosphors exhibit dazzling multicolor visible light emissions from different Ln3+ ions. The results indicate that the as-obtained Ln3+ doped BTO phosphors may be potentially utilized in LED devices and solid-state lighting. Furthermore, the Eu3+ and Er3+ co-doped BTO samples exhibit different DC and UC luminescence spectral profiles when excited at various UV, visible, or NIR wavelengths, revealing their eminent feasibility and great potential in anti-counterfeiting applications.

Fabrication and optical properties of garnet ceramics based on Y3-xScxAl5O12 doped with ytterbium and erbium.

Optical ceramics YSAG:Yb,Er with an average grain size of 6 ± 1 microns were fabricated by vacuum sintering of nanocrystalline powders of the compositions Y2.34Yb0.45Er0.09Sc0.20Al4.92O12, Y1.66Yb0.45Er0.09Sc1.00Al4.80O12 and Y0.96Yb0.45Er0.09Sc1.70Al4.80O12. The linear transmittance coefficients of the YSAG:Yb,Er ceramic samples exceed 80% in the visible and infrared regions. The refractive index of ceramics increased from 1.827 to 1.859 with an increase in scandium content. The effect of scandium cations at the dodecahedral site of the YSAG crystal lattice on the optical and luminescence characteristics of Yb3+ (2F7/2 and 2F5/2) and Er3+ (4I15/2, 4I13/2, 4F9/2 and 4S13/2) in wavelength ranges of 530-690 nm, 890-1080 nm, and 1430-1680 nm was revealed.

Significant Contribution of Deeper Traps for Long Afterglow Process in Synthesized Thermoluminescence Material

A promising candidate of long persistent Ca2 MgSi2 O7 :Dy3+ phosphor sample was well sintered via traditional high temperature solid-state synthesis technique and characterized in terms of crystal structure, particle size, phase composition and TL trapping parameters have briefly discussed using X-Ray Diffraction (XRD), Field Emission Scanning Electron microscopy (FESEM), Energy Dispersive X-ray (EDX) Spectroscopy and TL-Dosimetry Reader techniques. The XRD results revealed that it has formed in a single phase and tetragonal crystallography (Akermanite crystal structure) with a space group P4̅21m. All trapping parameters such as activation energy (E) (i.e. trap depth), order of kinetics (b) and frequency factor (s), and all these trapping parameters were calculated using Chen’s glow curve method. In this present paper, structural & thermal properties of synthesized phosphor are discussed in detail. We have clearly observed that the trapped electrons in the crystal lattice site and the self-trapped hole that both are responsible for crystal growth process. Deeper traps are highly helpful for increasing the long persistent duration and afterglow process.

The yellow spectral performances of Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals

2 at.% Dy3+: BaF2 and 2 at.% Dy3+/2 at.% RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 single crystals were grown by the Bridgman-Stockbarger method, and characterized by absorption, visible emission, and fluorescence decay curves. Also, relying on the excitation and emission spectra, decay curves at low temperature (77 K) for Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals have been measured. We found that Dy ions have at least three lattice sites in BaF2 crystal, and the lattice sites of Dy3+ ions can be reduced by co-doping with Gd3+, Y3+ or Lu3+ ions, where Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 single crystals can be considered as quasi-single lattice crystals. From visible fluorescence spectra, it was found that co-doping Gd3+ will increase the emission intensity of yellow light by 20 times, co-doping Y3+ will increase the emission intensity of yellow light by 30 times, and co-doping Lu3+ will increase the emission intensity of yellow light by 25 times. The calculated absorption cross-section, emission cross-section, and fluorescence lifetimes indicate that Dy3+: BaF2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF2 crystals especially, Dy3+/Y3+: BaF2 crystals are suitable to achieve yellow laser output.

Exact ground state energy of a system with an arbitrary number of dipoles at the sites of a regular one-dimensional crystal lattice

We consider a finite classical system of electric dipoles localized at the sites of a regular one-dimensional crystal lattice. It is shown that the ground state energy of such a system can be calculated exactly for an arbitrary number of dipoles. The expression for the ground state energy can be given in terms of special functions such as Riemann zeta functions and polygamma functions for any arbitrary number of dipoles, and reduces to the correct result in the thermodynamic limit as the number of dipoles tends to infinity. Simpler, but very accurate, approximate expressions for the ground state energy are also introduced.

Calcite Kinks Grow via a Multistep Mechanism.

The classical model of crystal growth assumes that kinks grow via a sequence of independent adsorption events where each solute transitions from the solution directly to the crystal lattice site. Here, we challenge this view by showing that some calcite kinks grow via a multistep mechanism where the solute adsorbs to an intermediate site and only transitions to the lattice site upon the adsorption of a second solute. We compute the free energy curves for Ca and CO3 ions adsorbing to a large selection of kink types, and we identify kinks terminated both by Ca ions and by CO3 ions that grow in this multistep way.

Extension of the Aggregation-Volume-Bias Monte Carlo Method to the Calculation of Phase Properties of Solid Systems: A Lattice-Based Cluster Approach.

The aggregation-volume-bias Monte Carlo method, which has been successful in the calculation of the formation free energies of liquid clusters, is extended to solid systems. This extension is motivated by early studies where disordered clusters are observed when the original method is applied at a temperature even far below the triple point. In order to avoid the formation of disordered aggregates, the insertion of particles is targeted directly toward those crystal lattice sites. Specifically, the insertion volume used to be defined as a spherical volume centered around a given target molecule is now restricted to be around each of the crystal lattice sites near a given target molecule. The free energies obtained for both liquid and solid clusters are then used to extrapolate bulk-phase information such as the chemical potential of the liquid and solid phases at coexistence. Using the temperature and pressure dependencies of the chemical potential information obtained for both liquid and solid phases, the location of the triple point can be determined. For Lennard-Jonesium, the results were found to be in good agreement with previous simulation studies using other approaches.

Structure induced modification on thermoelectric and optical properties by Mg doping in CuCrO2 nanocrystals

P-type semiconductors draw special attention because of its application in high-temperature thermoelectric devices and sensors. Oxide materials showing a negative temperature coefficient of resistance at high-temperatures make them good substitutes as one leg of the devices. Proper doping makes CuCrO2 a potential P-type semiconductor for TE application. The study incorporate Mg2+ for Cr3+ site in delafossite CuCrO2 crystal lattice. High-temperature solid-state reaction route has been chosen for the synthesis CuCrMgO2, by taking appropriate proportion of Cu2O, Cr2O3, and MgO. The structural studies were done by XRD, Raman analysis, FTIR, and SEM. CuCrMgO2 pellets with a thickness of 2 mm and a diameter of 13 mm were prepared for thermoelectric studies. By varying doping percentages, considerable changes in conductivity were observed. The highest conductivity of 1149.42 S/m was obtained for 1.5 wt% sample at 600 °C. It was observed that the electrical conductivity increased with the increase of doping percentages while the Seebeck coefficient decreased, which led to a maximum increase of 1.95 times in the power factor of CuCrO2. The maximum power factor of 1.2153 × 10−4 W/mK2 was calculated for 0.5 wt% doped sample at 600 °C. The electronic spectroscopic studies at ambient conditions reveal weak absorbance in the wavelength range of 300–400 nm for all samples. It is also found that increased absorbance, and direct optical band gap variation between 3.35 and 3.44 eV with doping.

Magnetization reversal driven by electron localization-delocalization crossover in the inverse spinel Co2VO4

Neutron diffraction, magnetization, and muon spin relaxation measurements, supplemented by density functional theory (DFT) calculations are employed to unravel temperature-driven magnetization reversal in inverse spinel ${\mathrm{Co}}_{2}{\mathrm{VO}}_{4}$. All measurements show a second-order magnetic phase transition at ${T}_{\mathrm{C}}=168\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to a collinear ferrimagnetic phase. Neutron diffraction measurements reveal two antiparallel ferromagnetic (FM) sublattices, belonging to magnetic ions on two distinct crystal lattice sites, where the relative balance between the two sublattices determine the net FM moment in the unit cell. As the evolution of the ordered moment with temperature differs between the two sublattices, the net magnetic moment reaches a maximum at ${T}_{\mathrm{NC}}=138\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and reverses its sign at ${T}_{\mathrm{MR}}=65\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The DFT results suggest that the underlying microscopic mechanism for the reversal is a delocalization of the unfilled $3d$-shell electrons on one sublattice just below ${T}_{\mathrm{C}}$, followed by a gradual localization as the temperature is lowered. This delocalized-localized crossover is supported by muon spectroscopy results, as strong ${T}_{1}$ relaxation observed below ${T}_{\mathrm{C}}$ indicates fluctuating internal fields.

Structural and morphological studies of Se doped SnTe thermoelectric material

Structural properties of pristine and 3% Se doped SnTe were studied for thermoelectric applications. The solvothermal method is used to synthesizematerials. Powder XRD was used to investigate the crystal structure of synthesized materials. Pristine SnTe has FCC structure with Fm-3m space group. Secondary phase of SnSe was observed in SnTe0.97Se0.03. Electron density maps confirm the uniform distribution of basis at the crystal lattice sites. The distribution of nanoparticles in both materials is depicted using FESEM micrographs. Crystallite size decreases after Se doping in SnTe. In Se doped SnTe, lattice strains, stacking faults, and dislocation densities all increase. Secondary phase, nanoparticle formation and distortion in crystal structure can scatter phonons. The scattering of phonons reduces lattice thermal conductivity. Therefore Se doped SnTe can be an efficient material for thermoelectric device fabrication.

Low temperature synthesis and influence of Ce3+ substitution on structural and magnetic properties of nanocrystalline cobalt ferrite using citrate precursor sol-gel method

Rare earth element Ce3+ substituted spinel cobalt ferrite, CoFe2-xCexO4 for (x = 0.0, 0.05, 0.10, 0.15, 0.20) is synthesized using an economical sol–gel technique. The X-ray diffraction analysis reveals that all samples have spinel symmetry indexed to Fd3m space group. Fullprof Rietveld analysis is performed to find out lattice parameters that increase monotonically due to induced lattice strains in samples. The crystallite size was determined to be 54.9 nm using Williamson-Hall plots. The morphological analysis of samples has been performed using SEM imaging. FTIR spectrum confirms octahedral and tetrahedral site occupancy by metal–oxygen bonds for all samples. The magnetic properties of samples refine with Ce3+ doping at iron site, with magnetization ranging from 23.59 to 57.68 emu/g and retentivity 17.14 to 24.08 emu/g. The Coercive field values drastically increased from 739 to 1912 Gauss. Thus, we have explored the influence of rare earth Ce3+ (1.14 Å) substitution at the Fe3+ site (0.55 Å) in CoFe2O4 crystal lattice for improvement of its structural and magnetic properties in this paper.

Enhancement of anisotropy energy of SmCo5 by ceasing the coupling at 2c sites in the crystal lattice with Cu substitution

SmCo5 and SmCo5−xCux magnetic particles were produced by co-precipitation followed by reduction diffusion. HRTEM confirmed the Cu substitution in the SmCo5 lattice. Non-magnetic Cu was substituted at “2c” site in the SmCo5 crystal lattice and effectively stopped the coupling in its surroundings. This decoupling effect decreased magnetic moment from SmCo5 (12.86 μB) to SmCo4Cu (10.58 μB) and SmCo3Cu2 (7.79 μB) and enhanced anisotropy energy from SmCo5 (10.87 Mega erg/cm3) to SmCo4Cu (14.05 Mega erg/cm3) and SmCo3Cu2 (14.78 Mega erg/cm3). Enhancement of the anisotropy energy increased the coercivity as its values for SmCo5, SmCo4Cu and SmCo3Cu2 were recorded as 4.5, 5.97 and 6.99 kOe respectively. Being six times cheaper as compared to Co, substituted Cu reduced the price of SmCo3Cu2 up to 2%. Extra 15% Co was added which not only enhanced the Mr value but also reduced the 5% of the total cost because of additional weight added to the SmCo3Cu2. Method reported in this work is most energy efficient method on the synthesis of Sm–Co–Cu ternary alloys until now.

Cluster Variation Method Analysis of Correlations and Entropy in BCC Solid Solutions

Solid solutions occur when multiple chemical species share sites of a common crystal lattice. Although the single site occupation is random, chemical interaction preferences bias the occupation probabilities of neighboring sites, and this bias reduced the entropy of mixing below its ideal value. Sufficiently strong bias leads to symmetry-breaking phase transitions. We apply the cluster variation method to explore solid solutions on body centered cubic lattices in the context of two specific compounds that exhibit opposite ordering trends. Employing density functional theory to model the energetics, we show that CuZn exhibits an order-disorder transition to the CsCl prototype structure, while AlLi instead takes the NaTl prototype structure, and we evaluate their temperature-dependent order parameters, correlations and entropies.

Catalytic activity of Ru supported on SmCeOx for ammonia decomposition: The effect of Sm doping

SmCeOx composite oxide with Sm3+ occupying Ce4+ site in CeO2 crystal lattice, prepared via citric acid complexation method, was loaded with 2 w% Ru by impregnation method and the as-prepared catalyst was then evaluated for ammonia decomposition. The results show that the partial substitution of Ce4+ by Sm3+ produces a positive effect on the catalyst performance and SmCeOx supported Ru exhibits a much higher low-temperature catalytic activity for ammonia decomposition compared with other supports such as Sm2O3, CeO2, and a physical mixture of Sm2O3 and CeO2. For example, the ammonia conversion is increased from 54.6% to 74.9% at a temperature of 400 ​°C and a space velocity of 3900 ml/gcat·h when CeO2 is replaced by Sm0.4Ce0.6O1.8. TEM and CO chemisorption investigations reveal that the excellent performance of Ru/SmCeOx catalyst is related to its high Ru dispersion. The results of BET, EPR and H2-TPR suggest that the partial substitution of Ce4+ with Sm3+ may induce the formation of oxygen vacancies and the high Ru dispersion can be attributed to the presence of large amount of single-electron trapped oxygen vacancies on the surface of SmCeOx, which have a strong interaction with Ru and thus Ru preferentially occupies the oxygen vacancies. This experimental observation is also supported by the DFT calculation result that Ru species adsorbed on the oxygen vacancy has a low adsorption energy.