Superionic phase transition in (NH4)2SeO4·2NH4HSeO4 single crystal at 378 K

Abstract

DTA, structural and electric conductivity investigations were made for (NH₄)₄H₂(SeO₄)₃ single crystals. A high-temperature phase transition at 378 K to a superionic phase was found. The phase is characterized by a high electrical conductivity (～4.10^?3 Ω^?1 cm^?1) and a low activation energy (0.11 eV).     

Thermoluminescence and ESR phenomena in X-ray irradiated mixed alkaline-alkaline earth metal sulfates—I

Abstract

Thermoluminescence (TL) and ESR phenomena induced by X-ray irradiation of the mixed samples of K₂SO₄ and alkaline earth metal sulfate (MgSO₄ or BaSO₄) were investigated in terms of the reactivities and the crystallogrpahic properties. A high intensive TL resulted from the diffusion of a small amount of Mg²⁺ into K₂SO₄ crystals. The amount formed of K₂Mg₂(SO₄)₃, langbeinite, compound had a maximum at the stoichiometric composition. From the ESR measurements, SO^? ₃ radicals were found to be easily formed in the langebeinite by excitation. Both the TL and the ESR phenomena were hardly observed in the K₂SO₄–BaSO₄ system due to little diffusion of Ba²⁺ with much larger radius than Mg²⁺. The results were mainly discussed on the basis of the radii of the component cations in these systems. In addition, the fundamental data as to the application to the ESR dosimetry were obtained.     

Part II: Effect of high energy proton beam fluence on the electrical studies of lithium gallium phosphate glass electrolyte doped with selenium ions

A series of glass samples, according to the formula (100 ? x) (0.5Li₂O ? 0.2Ga₂O₃ ? 0.3P₂O₅) + xSeO₂ (x?=?0, 2, 4, 6, 8, 10) and 12 mol.%, labeled as LGPS _x (x is the mole percent of SeO₂), were synthesized through melt quenching technique. All the LGPS _x samples were irradiated by a high energy proton (H⁺) beam of 3 MeV at fluence of 10¹⁴, 5 × 10¹⁴, and 10 × 10¹⁴ ions/cm². FTIR and Raman spectra indicated that SeO₂ acts either as a glass modifier (SeO ₃ ^2? ) or a glass former (SeO ₄ ^2? ), as the dose rate of beam fluence changes. The bulk conductivity of the highest conducting sample LGPS₁₀ irradiated at a beam fluence of 5 × 10¹⁴ ions/cm² was determined as 5.87 × 10^?04 S/cm at 303 K. The super curve in the normalized spectra of electrical modulus at different temperatures confirms that the LGPS samples follow the temperature-independent, frequency-dependent relaxation time before and after irradiation.     

Synthesis,Characterization and DNA Interaction Study of a New Oxovanadium (IV) Complex Containing Acetylacetone and Dicyandiamide as Ligands

ABSTRACT

A new oxovanadium (IV) complex [VO(acac)₂DCDA]H₂O (where acac = acetylacetonate; DCDA = dicyandiamide) was synthesized and characterized by elemental analysis, IR, UV, ESR, TG-DTA analysis and powdered XRD. The electronic and ESR spectral studies indicate the monomeric nature of the complex having distorted octahedral structure. The complex shows prominent emission peak at 485 nm and excitation peak at 355 nm. The cyclic voltammetry study shows irreversible process. DNA binding study of the complex with CT-DNA indicates nonintercalative mode with binding constant 2.063 × 10² M^?1.     

Thermodynamic properties of successive phase transitions in Rb2ZnBr4

Heat capacity measurements have given the following transition temperatures and entropies: 0.027 J K^?1mol^?1 at 76.5 K, 0.47 J K^?1mol^?1 at 111.7 K, and 0.048 J K^?1mol^?1 at 193.6 K. These are interpreted as “lock-in”, soft-mode, and “lock-in” transitions, respectively, from comparison with analogous results for Rb₂ZnCl₄ and K₂SeO₄. The N-IC transition was located at 347 K by DTA.     

Analysis of the ESR Spectrum of a Rhodium (II) Complex

Abstract

Rh(II) complexes are rather scarce¹ and often form dimeric structures, which are diamagnetic. The ESR spectra of definite Rh(II) species have so far been claimed for Rh in ZnWO₃ ², [Rh S₄C₄(CN)₄]^{2 ?}, ^3′4 [Rh(π-C₅H₅)₂]⁵, [(π-C₅H₅)Rh(π-C₂H₄)₂]⁺⁶, and an irradiation produced [RhCπ₂(CN)₄]^{2 ?} complex.⁷ A detailed analysis has been performed on the first², the second⁴ and the last⁷ complexes. The first system shows an almost axial symmetry and the unpaired electron has been assigned to the d_xy orbital² (the x,y,z axes are defined along the octahedral metal-ligand directions). The sulfur ligand complex and the dichlorotetracyano system have their unpaired electron in the d_Z ² orbital. ^4,7 In the course of studies ^8-10 on oxygenation of a Rh(I) complex, [RhCπ(C₈H₁₄)₂]₂, we observed ¹⁰ that a well defined ESR spectrum develops during the reaction in N,N′-dimethylacetamide (DMA) - lithium chloride media. For experimental detail, reference 10 should be consulted. The data summarized in the table refer to the spectrum B in that reference and are attributed to a Rh(II) species.     

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu²⁺-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu²⁺ lattice sites, Cu²⁺(I) and Cu²⁺(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: g_x ?=?2.0201?±?0.002, g_y ?=?2.0900?±?0.002, g_z ?=?2.1634?±?0.002, A_x ?=?(30?±?2)?×?10^?4?cm^?1, A_y ?=?(40?±?2)?×?10^?4?cm^?1 and A_z ?=?(154?±?2)?×?10^?4?cm^?1. It was found that Cu²⁺ enters the lattice substitutionally. The ground-state wavefunction of the Cu²⁺ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.     

ESR investigation of structure and dynamics of paramagnetic centres in lime mortars from Budinjak,Croatia

This study presents the preliminary results of investigation of the types and dynamics of paramagnetic centres in lime mortars from Sveta Petka church in Budinjak, Croatia, using Electron Spin Resonance (ESR) spectroscopy. The excavation in Budinjak discovered a very unique four lobed plan object Sveta Petka, with no additional finds or reliable historical records about the time of its construction. The lime mortars from the church were chosen for analysis in order to characterize the building material and to verify the site chronology by dating them. Lime mortar is valuable but problematic material for luminescence and radiocarbon dating. This type of material has not been dated before using ESR; therefore, careful studies are required to identify the useful paramagnetic centres. The ESR approach suggested in this work concentrates on a calcium carbonate signal. All samples were γ-irradiated in ⁶⁰C bomb with the doses of 1, 10, 20, 50, 80 and 100 kGy. In all spectra signals from Fe³⁺ and Mn²⁺ ions have been observed. Paramagnetic centres which give the ESR signals may be interpreted as CO₂^?, CO₃^?, CO₃^3?, HCO₃^2?, SO₂^?, SO₃^?, PO₂^? and PO₃^2? species. However, all spectra are complex and signals are interfering; therefore, computer resolution enhancement method will be needed in further research. The changes in ESR signals amplitude measured at magnetic field range about 3440–3450 G were analysed versus the dose of irradiation, using Mn²⁺ signals as a reference. Exponential growth of the curve and saturation for doses above 20 kGy were observed; therefore, irradiation with smaller doses is required. These preliminary studies will be helpful in future attempts of dating lime mortars by ESR method.     

Estimation of T1 for Co2+ ions from the temperature variation of the ESR linewidths for VO2+ in Cs2Co(SeO4)2·6H2O single crystals

The electron spin resonance of VO²⁺ is studied in single crystals of Cs₂M″ (SeO₄)₂·6H₂O (M″ = Zn, Co) from 290 to 77 K at ～ 9.45 GHz. The line broadening of VO²⁺ spectra on cooling the Cs₂Co(SeO₄)₂·6H₂O crystal is explained on the basis of host spin-lattice relaxation narrowing. T₁ for Co²⁺ is estimated to be ≈ 1.7 × 10^?12 sec. at 290 K.     

Effects of Gd<Superscript>3+</Superscript> doping on structural and dielectric properties of PZT (Zr:Ti = 52:48) piezoceramics

The purpose of this research is to study the effect of doping Gd into Pb(Zr_0.52Ti_0.48)O₃ ceramics prepared by solid state reaction. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole % Gd at which the unreacted oxides start to appear. The electron spin resonance (ESR) spectra of PGZT's indicate that Gd³⁺ can enter both A site of the perovskite structure instead of only A site as widely believed. The ESR peaks resonance shift towards low fields as the concentration is higher, which is due to the change in crystal field experienced by Gd³⁺ ions. At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising from Gd³⁺ (4f⁷, spin 7/2) ions at A site. The first set shows some fine structure having strong absorption peaks centered at 76.26 mT (g = 8.550). The second is a seven-peak spectrum centered at 206.01 mT (g = 3.165), which belongs to the Gd³⁺ ions at B sites. Furthermore, the overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g = 2.2818-2.1087) belong to Gd³⁺ of unreacted Gd₂O₃. The local environments of Gd³⁺ ions were verified from the calculated ESR spectra using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor g, zero-field splitting D and hyperfine tensor A.     

Spontaneous polarization in the RbD3 (SeO3)2 crystal

It has been experimentally shown for the first time that below T_c RbD₃ (SeO₃)₂ possesses spontaneous polarization of the order of 10^?4 μC cm^?2.     

Fundamental Concepts of Electron Spin Resonance Technique in the Determination of the Crystal Field Structure of O− 2 Ions in TiO2

Abstract

The basic principles of Electron Spin Resonance (ESR) as applicable in crystal field characterization of paramagnetic species has been outlined. Fundamental concepts of the precessional motion of electrons and their magnetic moments at resonance were developed. The theory of ESR based on the response of unpaired electron(s) as they undergo spin-spin or spin-lattice relaxation when subjected to strong external magnetic fields was examined. Ions of the O^? ₂ group adsorbed on TiO₂ were studied using a Varian Spectrometer. The resulting spectral diagrams obtained were used in calculating the g-factors which gave results for orthorhombic crystal symmetry for O^? ₂ ions in TiO₂.     

Mechanism of thermoluminescence in Sm- and Eu-doped barium sulphate

Thermoluminescence, TL emission spectra, ESR and optically excited luminescence of BaSO₄:Sm and BaSO₄:Eu were investigated. The optically excited luminescence studies showed that samarium ions were stabilized in the trivalent state in doped samples, and a fraction of these ions was reduced to the divalent state on γ-irradiation. These reduced ions were reoxidized on thermal annealing. Europium was found to be stabilized in the divalent form in BaSO₄:Eu phosphor, both before and after γ-irradiation. These results were further confirmed from the emission spectra of different glow peaks from BaSO₄:Sm and BaSO₄:Eu samples. The ESR spectra of these samples, recorded after γ-irradiation and various post-irradiation thermal annealings, revealed that anion radicals (such as SO₄^?, SO₃^?, SO₂⁺ and O₃^?) are formed on γ-irradiation and get annihilated at temperatures which corresponds to some of the glow peaks. An attempt is made to explain the results by a mechanism, suggested earlier for other impurity-doped BaSO₄ phosphors, in which holes released on thermal activation from anion radicals recombine with the electrons trapped at certain defect centres and the energy thus released is non-radiatively transferred to the impurity ions, which give their characteristic emission.     

Structure of the low-temperature phase of Rb3D(SeO4)2 by single-crystal neutron diffraction

Crystal structure of Rb₃D(SeO₄)₂ has been investigated at 25 K (below the transition temperature T_c=95.4 K) by single-crystal neutron diffraction. Accompanying the transition, the SeO₄ groups, which are all equivalent in the phase above the transition (space group A2/a), split into eight nonequivalent groups in a superlattice (a×2b×2c, space group A2) in the low-temperature phase. Based on the D atom positions obtained, each of the SeO₄ groups was identified to be in the state closer to a HSeO₄⁻ ion or to a SeO₄²⁻ ion and the dipole arrangement of SeO₄-D-SeO₄ dimer was revealed. This dipole arrangement has ‘ferri’ structure along the polar b-axis, but ‘antiferro’ structure in the plane perpendicular to the b-axis. These results are consistent with the characteristics found in the earlier dielectric measurements.     

Silicon negative ion implantation induced vacancy defects in thermally grown SiO2 thin films

ABSTRACT

Thermally grown SiO₂ thin films on a silicon substrate implanted with 100?keV silicon negative ions with fluences varying from 1?×?10¹⁵ to 2?×?10¹⁷ ions cm^?2 have been investigated using Electron spin resonance, Fourier transforms infrared and Photoluminescence techniques. ESR studies revealed the presence of non-bridging oxygen hole centers, E′-centers and P_b-centers at g-values 2.0087, 2.0052 and 2.0010, respectively. These vacancy defects were found to increase with respect to ion fluence. FTIR spectra showed rocking vibration mode, stretching mode, bending vibration mode, and asymmetrical stretching absorption bands at 460, 614, 800 and 1080?cm^?1, respectively. The concentrations of Si–O and Si–Si bonds estimated from the absorption spectra were found to vary between 11.95?×?10²¹ cm^?3 and 5.20?×?10²¹ cm^?3 and between 5.90?×?10²¹ cm^?3 and 3.90?×?10²¹ cm^?3, respectively with an increase in the ion fluence. PL studies revealed the presence of vacancies related to non-bridging oxygen hole centers, which caused the light emission at a wavelength of 720?nm.     

Effect of acids on the gamma-radiolysis of frozen aqueous systems of some organic compounds

Abstract

ESR spectra of γ-irradiated frozen aqueous solutions of a number of organic compounds such as alcohols, ether, acetone and tetrahydrofurans have been examined in the presence and absence of mineral acids such as H₂SO₄. The presence of the acid is found to cause an intensification of the organic radical ESR spectra as compared with the acid free solutions. Also, the presence of the organic compounds in frozen aqueous H₂SO₄ suppresses the formation of both H-atoms and SO₄ ^? radical ions. These results have been explained on the basis of reactions of the electrons and holes, or excitons, primarily formed by the action of radiation on the substrate ice.     

Influence of N‐Substitution on Electron Spin Resonance (ESR) Behavior of 2‐(2‐Nitrophenyl)‐1H‐benzimidazole Derivatives

Abstract

The synthesis of 2‐(2‐nitrophenyl)‐1H‐benzimidazole (1), 1‐benzoyl‐2‐(2‐nitrophenyl)‐1H ‐benzimidazole (2), and 1‐acetyl‐2‐(2‐nitrophenyl)‐1H‐benzimidazole (3) is reported. Stable radical anions (1 ^·?, 2 ^·?, and 3 ^·?) were generated by chemical reduction in DMSO and studied by ESR spectroscopy. The interpretation of the ESR spectra was done by means of computational simulation process. Hyperfine coupling constants were assigned by comparison with related compounds, and on the basis of calculation based on SCF INDO MO method in the unrestricted Hartree–Fock scheme.     

Electronic Absorption Spectrum of Fe3+ Doped in Ammonium Perchlorate Single Crystal

Abstract

Single crystals of Iron - doped ammonium perchlorate were grown at room temperature. The electronic absorption bands observed at room and liquid air temperatures have been assigned transitions from the ground ⁶A_1g state to the excited ⁴A_1g, ⁴E_g, ⁴T_1g and ⁴T_2g states. The crystal field parameters Dq = 870 cm^?1, B = 615 cm^?1 and C = 4.2 B are found to give a good fit to the observed band positions.     

Dielectric and AC ionic conductivity investigations in K3H(SeO4)2 single crystal

Optical observation under the polarizing microscope and DSC measurements on K₃H(SeO₄)₂ single crystal have been carried out in the temperature range 25-200 °C. It reveals a high-temperature structural phase transition at around 110 °C. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K₃H(SeO₄)₂ were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation σ(ω)=σ(0)+Aωⁿ, where ω is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO₄ groups, which provide more vacant sites in the crystal.     

Structure of paramagnetic defects in BaTiO3 and their light induced charge conversion

Abstract

We report the ESR of Nd³⁺ in BaTiO₃ and derive the electronic structure of its groundstate. – Among the light induced charge conversions found with ESR in nominally undoped BaTiO₃ crystals hole photoionization of Fe⁴⁺ is the most important. The process is increased by oxidizing the crystals. Some of the holes are trapped as O^? next to an unidentified acceptor. The trapping site of the remaining holes is ESR-silent.