1996 Effect of vanadium and cobalt ions on electrical conductivity and EPR in sodium borate glasses (original) (raw)
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2004
Glass systems with composition xTiO 2 ·(30 − x)Na 2 O·70B 2 O 3 (series I) and xTiO 2 ·(70 − x)B 2 O 3 ·30Na 2 O (series II) containing 2 mol% V 2 O 5 have been prepared (0 ≤ x ≤ 7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO 2+ ions have been recorded in the X-band (∼9.13 GHz) at room temperature. Spin Hamiltonian parameters, g || , g ⊥ , A ||, A ⊥ , the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been calculated. The increase in g || / g ⊥ with increase in TiO 2 content in series I shows that the octahedral symmetry of V 4+ O 6 complex is reduced, whereas in series II the octahedral symmetry is improved with increase in x. The decrease in P, in both the series, indicates that the 3d xy orbit expands with increase in mol% of TiO 2 . The molecular orbital coefficients, α 2 and γ 2 have been calculated by recording the optical transmission spectra in the range 500-850 nm. α 2 and γ 2 increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity σ, decreases and activation energy, W increases with increase in TiO 2 :Na 2 O ratio whereas with increase in TiO 2 :B 2 O 3 ratio the variation in σ and W is within experimental error.
Vanadyl ion Borate glasses Ionic conduction Optical properties
Electron paramagnetic resonance (EPR), optical properties and dc conductivity of xTiO 2 Á(30 À x)R 2 OÁ70B 2-O 3 and xTiO 2 Á(70 À x)B 2 O 3 Á30R 2 O (R = Li, K; 0 6 x 6 7, in mol%) glasses containing 2 mol% V 2 O 5 have been studied. Spin Hamiltonian parameters, g k , g \ , A k , A \ , the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been evaluated. Decrease in Dg k /Dg \ ratio with increase in TiO 2 content in TiO 2 ÁLi 2 OÁB 2 O 3 glasses show that the octahedral symmetry of V 4+ O 6 complex is improved; whereas in TiO 2 ÁK 2 OÁB 2 O 3 glasses, it is reduced with increase in x. The decrease in P, in both systems, indicates that the 3d xy orbit expands with increase in mol% of TiO 2 . The molecular orbital coefficients, a 2 and c 2 have been calculated by recording the optical transmission spectra in the range 400-850 nm. a 2 and c 2 increase with increase in x in all glasses expect KB glasses, which indicate that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity (r) decreases and activation energy (W) increases with increase in TiO 2 :R 2 O ratio in TiO 2 ÁR 2 OÁB 2 O 3 glasses whereas with increase in TiO 2 :B 2 O 3 ratio in TiO 2-ÁB 2 O 3 ÁR 2 O glasses the variation in r and W is within experimental error.
Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX Á (0.30Àx)M 2 O Á 0.70B 2 O 3 (M=Na or K; X=Cl or Br) (0:01pxp0:10) containing 2.0 mol% of V 2 O 5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO 2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (a 2 and g 2 ) have been calculated. It is observed that in KX Á K 2 O Á B 2 O 3 (X=Cl or Br) glasses, the tetragonal nature of V 4+ O 6 complex decreases with KBr for xX0:05: An increase in the 2KX:K 2 O ratio (xX0:05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX Á Na 2 O Á B 2 O 3 (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M 2 O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, L th : It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10 À6 O À1 m À1 at low temperatures and 10 À4 O À1 m À1 at high temperatures. In MCl Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content. r
Physica B-condensed Matter, 2003
Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX Á (0.30Àx)M 2 O Á 0.70B 2 O 3 (M=Na or K; X=Cl or Br) (0:01pxp0:10) containing 2.0 mol% of V 2 O 5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO 2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (a 2 and g 2 ) have been calculated. It is observed that in KX Á K 2 O Á B 2 O 3 (X=Cl or Br) glasses, the tetragonal nature of V 4+ O 6 complex decreases with KBr for xX0:05: An increase in the 2KX:K 2 O ratio (xX0:05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX Á Na 2 O Á B 2 O 3 (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M 2 O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, L th : It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10 À6 O À1 m À1 at low temperatures and 10 À4 O À1 m À1 at high temperatures. In MCl Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content. r
Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX Á (0.30Àx)M 2 O Á 0.70B 2 O 3 (M=Na or K; X=Cl or Br) (0:01pxp0:10) containing 2.0 mol% of V 2 O 5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO 2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (a 2 and g 2 ) have been calculated. It is observed that in KX Á K 2 O Á B 2 O 3 (X=Cl or Br) glasses, the tetragonal nature of V 4+ O 6 complex decreases with KBr for xX0:05: An increase in the 2KX:K 2 O ratio (xX0:05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX Á Na 2 O Á B 2 O 3 (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M 2 O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, L th : It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10 À6 O À1 m À1 at low temperatures and 10 À4 O À1 m À1 at high temperatures. In MCl Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr Á M 2 O Á B 2 O 3 (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content. r
DC electrical conduction in strontium vanadium borate glasses
Materials Science Poland, 2020
A series of borate glasses with the composition x(SrO)•(50-x)V 2 O 5 •0.5(B 2 O 3) where x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by melt-quenching technique. The non-crystalline nature of the glasses has been established by XRD studies. Room temperature density and DC electrical conductivity of the samples were investigated in the temperature range of 300 K to 443 K. The molar volume and oxygen packing density (OPD) were estimated. The results show that the density, molar volume and OPD decrease with the increasing of SrO mole fraction. The DC electrical conductivity data has been analyzed in the light of Mott's small polaron hopping (SPH) model and the activation energies were estimated. The conductivity was observed to rapidly fall and activation energy was found to increase when SrO was incorporated into the glass network. This may indicate that Sr + ions have not contributed to the total conductivity and the observed conductivity may be of polaronic type only, which is due to the hopping of electrons between multivalent states of vanadium. Various small polaron hopping parameters such as small polaron radius, r p , effective dielectric constant, p , polaron band width, J, optical phonon frequency, υ o , small polaron coupling constant, γ p , density of states at Fermi level, N(E F) were estimated and discussed.
EPR study of vanadyl ion in CoO · PbO · B2O3 glasses
Journal of Non-Crystalline Solids, 1996
Glasses with composition xCoO. (0.4 -x)PbO • 0.6B203 containing 1.0 mol% and 2.0 mol% VzO 5 have been prepared over the range O _< x < 0.20. The electron paramagnetic resonance spectra of VO 2+ of these glasses have been measured in the X-band (~ 9.3 GHz) at room temperature (RT ~ 300 K). Glasses with 1.0 mol% of V20 ~ were prepared by melting at 1173 K and 1373 K. Spin Hamilton±an parameters gJl' g-' AJI' A±, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. It is found that these parameters are independent of the temperature of the melt. Values of gtl' P decrease; value of K increases and value of g •, Akl, A ± are constant when V205 is increased from 1.0 mol% to 2.0 mol% in the binary lead borate glass, gkl' g ± ' All' A ±, P and K change from 1.922 + 0.001 to 1.927 ± 0.001, 1.968 + 0.001 to 1.973 ± 0.001, (166.9 _ 1.0) × 10 -4 Gin-J to (165.1 _+ 1.0) × 10 _4 Cm-i, (58.8 ± 1.0) X 10 -4 Cm -I to (62.6+1.0)×10 -4 Cm -~, 117.6X10 -4 Cm -1 to 111.2×10 -4 Cm i and 0.7614 to 0.8270, respectively, showing that tetragonal distortion of the V4+06 complex increases with increase in the CoO:PbO ratio. It is also found that the increase in CoO:PbO ratio results in an expansion of the 3dx ,, orbit of unpaired electrons in the vanadium ion and that the spin Hamilton±an parameters do not depend on the value of theoretical optical basicity.
Electron paramagnetic resonance study of vanadyl ions in Nal-Na2O-B2O3 glasses
Journal of Materials Science Letters, 1995
Glasses with the composition xCoO.(lx)(Zn0.2B203) have been prepared in the COO concentration range 0 < x < 0.24 containing 2 mol% V 2 0 5 . Electron paramagnetic resonance (EPR) spectra of V02+ of these glasses have been measured at the X-band frequency v Y 9.14 GHz, at room temperature and at liquid-nitrogen temperature. Spin-Hamiltonian parameters of the V02+ ions have been calculated. It is found that for x < 0.15 the octahedral symmetry of the V4+ site is improved. Parts of these glasses were annealed at 373 and 573 K for 2 h and EPR spectra were recorded and analysed. Theoretical optical basicity values of the samples were calculated and it was found that the predictions made by these calculated values are in agreement with the experimental findings.