Defect engineering, microstructural examination and improvement of ultrafast third harmonic generation in GaZnO nanostructures: a study of e-beam irradiation.

Electron beam induced effects on defect engineering and structural, morphological and optical properties of Ga doped ZnO (GaZnO) nanostructures for improved ultrafast nonlinear optical properties are presented. A microstructural analysis was carried out based on the Scherrer, Williamson-Hall, and size-strain models. All three models reveal a peak broadening effect upon electron beam irradiation (EBI) and the crystallite size of the films shows a decrease of 30% compared to unirradiated nanostructures. The decrease in intensity, variation in the peak position and broadening of the Raman E2H mode confirm that the EBI treatment introduces disorder into the nanostructures. The interband gap emissions observed in photoluminescence spectra are primarily due to defect-related emissions originating from intrinsic defects such as Zni, Oi, VZn, VO, VZn+, VO+ and OZn. The O1s core-level spectra show that the peak related to oxygen vacancy defects is suppressed upon EBI. Surface morphology studies reveal that the nucleation barriers of GaZnO nanostructures are reduced upon irradiation treatment resulting in a coalescence mechanism. Third harmonic generation studies show that higher electron-beam doses lead to the occurrence of enhanced THG signals due to a drastic change in the occupation of localized defect levels. Thermally induced nonlinear optical studies depict an improved χ(3) of 1.71 × 10-3 esu upon irradiation due to enhanced FCA induced TPA mechanism and non-radiative transitions which indicates the credibility of the grown films in photonic devices.

N→Sn-Coordinated Stannaoxidoborates Containing a SnB4O6 Unit.

We report here the synthesis of new N→Sn-coordinated stannaoxidoborates H[LSnB4O6R4] {L = [2,6-(Me2NCH2)C6H3](-) and R = Ph (6), 4-Br-Ph (7), 3,5-(CF3)2-Ph (8), and 4-CHO-Ph (9)} containing a nonsymmetric SnB4O6 unit. Compounds 6-9 represent new derivatives of the pentaborates [B5O6R4](-) in which the central boron is substituted by a tin atom. Compounds 6-9 were characterized by means of elemental analysis, electrospray ionization mass spectrometry, and NMR spectroscopy and in the case of 6-8 also by single-crystal X-ray diffraction analysis. The structures of N→Sn-coordinated stannaoxidoborates 6-8 consist of a spirobicyclic arrangement, with two six-membered SnB2O3 rings at the tin atom providing the new stannaoxidoborate [LSnB4O6R4](-) motif, which is compensated for by the proton atom coordinated to the Me2N group of the ligand L. The linear and thermal properties of 6-9 were studied with the help of electronic absorption spectra and differential scanning calorimetry. In addition, the presence of the nonsymmetric stannaoxidoborate SnB4O6 unit in 6, 7, and 9 prompted us to investigate their second-order nonlinear-optical properties.

Structural, electronic, and optical features of CuAl(S(1-x)Se(x))2 solar cell materials.

Detailed first-principles calculations of the structural, electronic, and optical properties of solid solutions of the promising solar cell material CuAl(S(1-x)Se(x))2 over the whole range of Se concentration from x = 0 to x = 1 were performed. It was established that the calculated lattice parameters, band gap, and anisotropic refractive indices vary linearly with the Se concentration. The obtained linear dependences allow for reliable estimations of all these quantities for any value of x, which determines the solid solution composition. The calculated results were compared with the experimental data available for x = 0, 0.5, and 1.0; very good agreement was demonstrated, which gives confidence in the properties calculated for other Se concentrations (x = 0.25, 0.75). The findings from the present paper can be used in a straightforward way for the successful production of CuAl(S(1-x)Se(x))2 mixed compounds with desired optoelectronic parameters, which are defined by the composition-tuned mobility of the charge carriers in the upper valence band and the conduction band. Extension of the presented approach to other materials is also possible.

Dicyanobenzene and dicyanopyrazine derived X-shaped charge-transfer chromophores: comparative and structure-property relationship study.

A series of novel X-shaped push-pull compounds based on benzene-1,2-dicarbonitrile has been designed, synthesized and further investigated by X-ray analysis, electrochemistry, absorption and emission spectra, SHG experiment and quantum-chemical calculations. The obtained data were compared with those for isolobal 5,6-disubstituted pyrazine-2,3-dicarbonitriles. Structure-property relationships were elucidated. The extension, composition and planarization of the π-linker used as well as the electron-withdrawing ability of both dicyano-substituted acceptor units affect the linear and nonlinear properties of the target charge-transfer chromophores most significantly.

Specific features of the electronic structure of a novel ternary Tl3PbI5 optoelectronic material.

A novel Tl3PbI5 crystal has been studied both experimentally and theoretically. Complex measurements of the X-ray photoelectron core-level and valence-band spectra for the pristine and Ar(+)-ion irradiated surfaces of a Tl3PbI5 single crystal grown by the Bridgman-Stockbarger method were performed in order to clarify their principal properties (charge carriers mobility, effective inter-band distances, effective absorption etc.) relevant for optoelectronic applications. The principal role of two heavy cations - Tl and Pb - is explored. The X-ray photoelectron spectroscopy results reveal a high chemical stability of the Tl3PbI5 single crystal surface which makes it very promising for technological applications. Theoretical band-structure calculations for the Tl3PbI5 compound reveal that the I 5p states dominate in the top of the valence band and play a crucial role in the formation of the optical features and charge carrier mobility. The bottom of the Tl3PbI5 valence band is formed mainly by the admixture of Tl 6s and Pb 6s states, while the unoccupied Pb 6p and Tl 6p states dominate at the bottom of the conduction band. The band energy dispersion related to effective masses and the charge carrier mobility is studied in detail. Crucially, the theoretical calculations reveal an indirect band gap for Tl3PbI5, which indicates a strong influence of the electron-phonon interaction on the observed optoelectronic features. The temperature measurements of the fundamental absorption have shown that the band energy gap of Tl3PbI5 increases from 2.29 to 2.39 eV when the temperature changes from 300 to 100 K.

Searching for better X-ray and γ-ray photodetectors: structure-composition properties of the TlPb2Br5-x I x quaternary system.

Developing X-ray and γ-ray detectors with stable operation at ambient temperature and high energy resolution is an open challenge. Here, we present an approach to search for new detector materials, combining binary photodetector compounds. More specifically, we explore quaternary TlPb2Br5-x I x compositions, relying on materials synergy between TlBr, TlI, and PbI2 photodetectors. We discover a broad solid solution in the TlPb2Br5-'TlPb2I5' section, which can be derived from a new quaternary compound, TlPb2BrI4, by partial substitution of Br by I atoms on the 4c site or by replacement of I by Br atoms on the 16l site. We carry out a thorough crystallographic analysis of the new TlPb2BrI4 compound and prepare a high-quality standardized structure file. We also complete the phase diagram of the TlPb2Br5-'TlPb2I5' section, based on 21 alloys. Furthermore, we synthesize a series of high quality centimeter-sized TlPb2Br5-x I x single crystals (x = 2, 2.5, 3, 3.5, 4, 4.5) by the Bridgman-Stockbarger method and study their structure and properties using a combination of experimental techniques (X-ray diffraction, X-ray photoelectron spectroscopy, and absorption spectroscopy) and theoretical calculations.

Dispersion of linear and nonlinear optical susceptibilities and the hyperpolarizability of 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole.

As a starting point for our calculation of 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole we used the XRD data obtained by C. Liu, Z. Wang, H. Xiao, Y. Lan, X. Li, S. Wang, Jie Tang, Z. Chen, J. Chem. Crystallogr., 2009 39 881. The structure was optimized by minimization of the forces acting on the atoms keeping the lattice parameters fixed with the experimental values. Using the relaxed geometry we have performed a comprehensive theoretical investigation of dispersion of the linear and nonlinear optical susceptibilities of 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole using the full potential linear augmented plane wave method. The local density approximation by Ceperley-Alder (CA) exchange-correlation potential was applied. The full potential calculations show that this material possesses a direct energy gap of 3.4 eV for the original experimental structure and 3.2 eV for the optimized structure. We have calculated the complex's dielectric susceptibility ε(ω) dispersion, its zero-frequency limit ε(1)(0) and the birefringence. We find that a 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole crystal possesses a negative birefringence at the low-frequency limit Δn(0) which is equal to about -0.182 (-0.192) and at λ = 1064 nm is -0.193 (-0.21) for the non-optimized structure (optimized one), respectively. We also report calculations of the complex second-order optical susceptibility dispersions for the principal tensor components: χ(ω), χ(ω) and χ(ω). The intra- and inter-band contributions to these susceptibilities are evaluated. The calculated total second order susceptibility tensor components at the low-frequency limit |χ(0)| and |χ(ω)| at λ = 1064 nm for all the three tensor components are evaluated. We established that the calculated microscopic second order hyperpolarizability, ß(ijk), the vector component along the dipole moment direction, at the low-frequency limit and at λ = 1064 nm, for the dominant component |χ(ω)| is 4.99 × 10(-30) esu (3.4 × 10(-30) esu) and 7.72 × 10(-30) esu (5.1 × 10(-30) esu), respectively for the non-optimized structure (optimized structure).

Peculiarities of the environmental influence on the optical properties of push-pull nonlinear optical molecules: a theoretical study.

Gas-phase geometry optimization of NLO-active molecules is one of the standard approaches in the first principle computational methodology, whereas the important role of the environment is usually not considered during the evaluation of structural parameters. With a wide variety of environmentally influenced models in most cases only the high quality single point calculations are prepared. Among different approaches, the most used polarizable continuum model (PCM) seems to be promising. In this study, we have compared the electronic properties of gas-phase optimized geometries of imidazole-derived push-pull compounds with those optimized using PCM solvation approach including CH(2)Cl(2) and PMMA as media. We have focused particularly on the linear optical properties of investigated molecules, namely on the UV-vis absorption spectra. The analysis of presented results shows the applicability of the different quantum chemical (QC) methods for the UV-vis spectra calculations of linear NLO molecules. Herein we also present the need of molecule geometry optimization affected by the environment. Following the performed calculations, the electronic properties of gas-phase optimized molecules give conformable results with respect to those obtained by more time-consuming continuum optimizations. All computational data are supported by experimental investigations.

Density functional calculations of the electronic structure of 3-phenylamino-4-phenyl-1,2,4-triazole-5-thione.

Starting with the X-ray diffraction data on the 3-phenylamino-4-phenyl-1,2,4-triazole-5-thione compound obtained by Wang et al. [Molecules, 2009, 14, 608], we have optimised the atomic positions by minimization of the forces acting on the atoms using a full potential linear augmented plane wave method within density-functional theory along with the generalized gradient approximation (GGA) by Perdew, Burke and Ernzerhof (PBE) exchange-correlation potential. In addition, for the electronic band-structure and the calculation of the gap the Engel-Vosko (EV-GGA) scheme has applied. The full potential calculations show that the valence band maximum (VBM) is located at the Gamma point and the conduction band minimum (CBM) is located at the Z point of the Brillouin zone resulting in an indirect energy gap of 3.1 eV. The upper VBM is mainly formed by S-p states while the lower CB has mainly C-p states character. Thus the S-p states in the upper valence band and the C-p states in the lower conduction band have a significant effect on the energy band gap. We present an analysis of the partial densities of states which gives useful information on hybridization and the orbital character of the states. We have calculated the bond lengths and bond angles and find better agreement with the experimental data than the density functional theory calculations at B3LYP/6-311G** and PBE1PBE/6-311G** levels of theory by the Berny method within the Gaussian 03 software package. This is attributed to the fact that the values obtained by these methods belong to the isolated molecule in the gas-phase whereas the experimental and the full potential linear augmented plane wave method values are attributed to the molecule in the solid state.

Optical operation by chromophores featuring 4,5-dicyanoimidazole embedded within poly(methyl methacrylate) matrices.

We have studied photoinduced absorption, birefringence, and optical second-harmonic generation in poly(methyl methacrylate) (PMMA) films doped by organic chromophores featuring 4,5-dicyanoimidazole in the weight content equal to 5%. The chromophores indicated as IM1-IM6 were synthesized from 2-bromo-1-methylimidazole-4,5-dicarbonitrile by either nucleophilic substitution or Suzuki-Miyaura cross-coupling reaction. The samples were obtained as films of several micrometers thickness by the spin-coating method on a quartz substrate. Measurements of the optically induced birefringence were done by the Senarmont method at wavelength 1150 nm, and photoinduced absorption was studied in the spectral range 250-700 nm under optical treatment by 300 mW cw 532 nm laser. Photoinduced optical effects were studied by bicolor 1064 and 532 nm coherent laser pulses. The maximal changes were observed for the ratio between fundamental and writing beam intensities equal to about 7:1. To interpret the observed experimental measurements, theoretical simulations of photoinduced optical properties were performed by quantum chemical computational methods.

DFT modeling of thermoelectric and optical features of novel MgxSn1-xSe (x = 6%, 12% & 18%).

We explore influence of Mg alloying effect on electronic band structure dispersion and thermoelectric properties of tin chalcogenide materials. Based on density functional theory (DFT) within a framework of full potential linearized augmented plane wave method (FP-LAPW), we evaluate the energy band structure and optical properties of MgxSn1-xSe (x = 6%, 12% and 18%) materials. Moreover, we extend our calculations to simulate the electrical transport properties using Boltzmann transport theory. Within the approximations employed in our calculations the theoretically predicted band energy gap values and the temperature dependence of electrical transport properties of MgxSn1-xSe compounds revealed that the Mg-alloying have enhanced thermoelectric features. To verify the quality of calculations the comparison with the experimental absorption spectra are presented. The better thermoelectric performance in MgxSn1-xSe is expected to occur for all doping concentrations, however 18% Mg-doped material exhibits higher value of Seebeck coefficient and lower thermal conductivity which is suggestive that at higher Mg concentration the holes become dominant over electrons and hence make these materials to be more promising candidates for their use in thermoelectric power generation and in cooling devices.

Band structure, density of states, and optical susceptibilities of a novel lithium indium orthoborate Li3InB2O6.

By use of the structural parameters of the single crystal lithium indium orthoborate obtained by Penin et al. (Solid State Sci. 2001, 3, 461-468), from X- ray diffraction data, we present a first-principle study of the electronic structure and the linear optical properties for the novel lithium indium orthoborate Li3InB2O6. A full-potential linear augmented plane wave method within density functional theory with the Engel-Vosko exchange correlation was used. This compound has a wide direct energy band gap of about 3.8 eV with both the valence band maximum and conduction band minimum located at the center of the Brillouin zone. Our calculations of the partial density of states shows that the upper valence band originates predominantly from the O-p, B- p, and In-p states, and the lower conduction band is dominated by the O-s/p, In-p, and B-p states. Thus the O-p states in the upper valence band and lower conduction band has a significant effect on the energy band gap dispersion. The uniaxial anisotropy [deltaepsilon=(epsilon0zz-epsilon0xx)/epsilon0tot] is about -0.041.

X-ray diffraction, crystal structure, and spectral features of the optical susceptibilities of single crystals of the ternary borate oxide lead bismuth tetraoxide, PbBiBO4.

The all-electron full-potential linearized augmented plane-wave method has been used for an ab initio theoretical study of the band structure, the spectral features of the optical susceptibilities, the density of states, and the electron charge density for PbBiBO4. Our calculations show that the valence-band maximum (VBM) and conduction-band minimum (CBM) are located at the center of the Brillouin zone, resulting in a direct energy gap of about 3.2 eV. We have synthesized the PbBiBO4 crystal by employing a conventional solid-state reaction method. The theoretical calculations in this work are based on the structure built from our measured atomic parameters. We should emphasize that the observed experimental X-ray diffraction (XRD) pattern is in good agreement with the theoretical one, confirming that our structural model is valid. Our calculated bond lengths show excellent agreement with the experimental data. This agreement is attributed to our use of full-potential calculations. The spectral features of the optical susceptibilities show a small positive uniaxial anisotropy.

Ab initio calculation of the electronic band structure, density of states and optical properties of alpha-2-methyl-1-nitroisothiourea.

The electronic and optical properties of alpha-2-methyl-1-nitroisothiourea have been studied using a full potential linear augmented plane wave method within density-functional theory along with the Engel-Vosko exchange correlation function. The structural data obtained by Vasil'ev et al. [Vasil'ev, A. D.; Astakhov, A. M.; Gelemurzina, I. V.; Stepanov, R. S. Dokl. Chem. 2001, 379, (4-6), 232-235; translated from Dokl. Akad. Nauk 2001, 379 (6), 781-784] from X-ray diffraction was used. Our calculations show that the valence band maximum (VBM) is located at the T and the conduction band minimum (CBM) is located at the R point of the Brillouin zone, resulting in an indirect energy gap of 3.1 eV. The calculated partial density of states shows that the upper valence band and the lower conduction band arise predominantly from the O-p, N-p and S-p states. The compound has a large uniaxial dielectric anisotropy and a large negative birefringence.

X-ray diffraction, X-ray photoelectron spectra, crystal structure, and optical properties of centrosymmetric strontium borate Sr2B16O26.

We report results of X-ray diffraction (XRD) and valence band X- ray photoelectron (VB-XPS) spectra for strontium borate Sr(2)B(16)O(26). The X-ray structural analysis shows that the single crystals of Sr(2)B(16)O(26) crystallize in the monoclinic space group P2(1)/c with a = 8.408(1) A, b = 16.672(1) A, c = 13.901(2) A, beta = 106.33(1) degrees , and Z = 4. The crystal structure consists of a 3D network of the complex borate anion [B(16)O(20)O(12/2)](4-), formed by 12 BO(3) triangles and four BO(4) tetrahedra, which can be viewed as three linked [B(3)O(3)O(4/2)](-) triborate groups bonded to one pentaborate [B(5)O(6)O(4/2)](-) group and two BO(3) triangles. Using this structure, we have performed theoretical calculations using the all-electron full potential linearized augmented plane wave (FP-LAPW) method for the band structure, density of states, electron charge density, and the frequency-dependent optical properties. Our experimental VB-XPS of Sr(2)B(16)O(26) is compared with results of our FP-LAPW calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma of the Brillouin zone (BZ) resulting in a direct energy gap of about 5.31 eV. Our measured VB-XPS show reasonable agreement with our calculated total density of states for the valence band that is attributed to the use of the full potential method.

X-ray photoelectron spectrum and electronic properties of a noncentrosymmetric chalcopyrite compound HgGa(2)S(4): LDA, GGA, and EV-GGA.

An all electron full potential linearized augmented plane wave method has been applied for a theoretical study of the band structure, density of states, and electron charge density of a noncentrosymmetric chalcopyrite compound HgGa(2)S(4) using three different approximations for the exchange correlation potential. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma resulting in a direct energy gap of about 2.0, 2.2, and 2.8 eV for local density approximation (LDA), generalized gradient approximation (GGA), and Engel-Vosko (EVGGA) compared to the experimental value of 2.84 eV. We notice that EVGGA shows excellent agreement with the experimental data. This agreement is attributed to the fact that the Engel-Vosko GGA formalism optimizes the corresponding potential for band structure calculations. We make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. We find that there is a strong covalent bond between the Hg and S atoms and Ga and S atoms. The Hg-Hg, Ga-Ga, and S-S bonds are found to be weaker than the Hg-S and Ga-S bonds showing that a covalent bond exists between Hg and S atoms and Ga and S atoms.

Synthesis and characterization of KTiOPO4 nanocrystals and their PMMA nanocomposites.

KTiOPO(4) (KTP) nanocrystals have been synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) and ethylene glycol (EG) as chelating and sterification agents, respectively. Orthorhombic KTP has been obtained by calcination at 1073 K for several hours. Differential thermal and thermogravimetric (DTA-TG) analyses have been used to study the optimized heat treatment used on the precursor powder to obtain KTP nanocrystals. X-ray powder diffraction (XRD) studies on the thermally treated precursor powders indicated that nanocrystals began to crystallize at 923 K. Nanocrystals with a size dispersion distribution that fit to a lognormal function centered at 25 nm were observed by electronic microscopy. KTP nanocomposites were prepared by embedding nanocrystals in poly(methyl methacrylate) (PMMA). The photoinduced second-order susceptibility parameter and the piezo-optical coefficient were measured for the KTP nanocomposites. The optimal conditions for the generation of the frequency-doubled second harmonic generation were recorded at 391 K, and at a fundamental laser wavelength of 1064 nm and under additional treatment by polarized UV light, provided the maximum value obtained of 3.23 pm V(-1). The piezo-optical coefficients were recorded at room temperature under photoinduced treatment by a UV laser beam; the maximum value achieved was 0.673 x 10(-14) m(2) N(-1) at a pump-probe delaying time of 160 s.

Dispersion of linear and nonlinear optical susceptibilities in calcium neodymium oxyborate Ca4NdO(BO3)3-LDA versus GGA.

We have performed ab inito theoretical calculations of the electronic structure and the linear and nonlinear optical susceptibilities for calcium neodymium oxyborate Ca4NdO(BO3)3 using two approximations for the exchange correlation (XC) potentials, the local density approximation (LDA) and the generalized gradient approximation (GGA). Our calculations show that this compound is metallic-like, with density of states at the Fermi energy E(F), N(E(F)), of 5.95 and 10.33 states/Ry-cell or bare electronic specific heat coefficients of 1.03 and 1.79 mJ/mol-K2 for LDA and GGA, respectively. The overlap between the valence and conduction bands is strong, resulting in metallic behavior. We found that Nd-s/p/d, Ca-s/p, B-p, and O-s/p states controlled the overlapping around E(F). The effect of LDA and GGA on the band structure, density of states, and linear optical properties is very small, while for the nonlinear optical properties, it is very pronounced. Our calculations show that χ(111)(2)(ω) is the dominant component for both LDA and GGA. We find opposite signs of the contributions of the 2ω and 1ω inter/intraband to the real and imaginary parts for the dominant component throughout the wide optical frequency range.

Synthesis, IR, UV-vis spectra, x-ray diffraction and band structure of a non-centrosymmetric borate single-crystal CaBiGaB(2)O(7).

A non-centrosymmetric borate, CaBiGaB(2)O(7), has been grown by a solid-state reaction method at a temperature below 700 °C. The single-crystal x-ray structural analysis has shown that it crystallizes in the tetragonal space group [Formula: see text] with a = 0.7457(1) nm, c = 0.4834(1) nm, Z = 2. It has a three-dimensional (3D) structure in which [B(2)O(7)](8-) groups are bridged by [GaO(4)](5-) tetrahedra through shared O atoms to form 2D [Formula: see text] layers that are further linked by Bi(3+)/Ca(2+) cations giving rise to the final 3D framework. The IR spectrum confirms the presence of [BO(4)](5-) groups and the UV-vis diffuse reflectance spectrum shows that the optical band gap is about 2.9 eV. This value is compared with our band structure calculations using the full potential linearized augmented plane wave approach within the framework of the Engel-Vosko GGA formalism.

Structural investigations on PbO-Sb(2)O(3)-B(2)O(3):CoO glass ceramics by means of spectroscopic and dielectric studies.

PbO-Sb(2)O(3)-B(2)O(3) glasses mixed with different concentrations of CoO (ranging from 0 to 2.0 mol%) were crystallized. The samples were characterized by x-ray diffraction, scanning electron microscopy and differential scanning calorimetric techniques. The x-ray diffraction and scanning electron microscopic studies have revealed the presence of CoSb(2)O(6), Co(2.33)Sb(0.67)O(4), Pb(5)Sb(2)O(8),Pb(3)(SbO(4))(2), PbB(4)O(7) and Co(3)O(4) crystalline phases in these samples. The DSC studies have indicated the spreading of the crystallization from the inside to the surface of the samples as the concentration of the crystallizing agent is increased. The IR and Raman spectroscopic studies have pointed out the existence of conventional BO(3), BO(4), SbO(4) and also Co(III)-O structural units in the glass ceramic samples. These studies have further indicated the decreasing concentration of symmetrical structural vibrational groups with increase in the concentration of CoO. The results of various studies, namely dielectric properties over a range of frequency and temperature, photo-induced birefringence, optical absorption, fluorescence and magnetic susceptibility at room temperature of PbO-Sb(2)O(3)-B(2)O(3):CoO glass ceramics, have also been reported. The variations observed as a function of the concentration of crystallizing agent in all these properties have been analyzed in the light of different oxidation states and environments of cobalt ions in the glass ceramic network.