Mixed alkali effect in Li{sub 2}O-Na{sub 2}O-B{sub 2}O{sub 3} glasses containing Fe{sub 2}O{sub 3}-An EPR and optical absorption study

Journal Article · Thu Sep 14 04:00:00 EDT 2006 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2006.02.028· OSTI ID:20895266

Sreekanth Chakradhar, R P ^[1]; Yasoda, B ^[2]; Rao, J Lakshmana ^[2]; Gopal, N O ^[2]

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1. Department of Physics, Indian Institute of Science, Bangalore 560 012 (India)
2. Department of Physics, Sri Venkateswara University, Tirupati 517 502 (India)

This paper reports the interesting results on mixed alkali effect (MAE) in xLi{sub 2}O-(30-x)Na{sub 2}O-69.5B{sub 2}O{sub 3} (5 {<=} x {<=} 28) glasses containing Fe{sub 2}O{sub 3} studied by electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra in these glasses exhibit three resonance signals at g = 7.60, 4.20 and 2.02. The resonance signal at g = 7.60 has been attributed to Fe{sup 3+} ions in axial symmetry sites whereas the resonance signal at g = 4.20 is due to isolated Fe{sup 3+} ions in rhombic symmetry site. The resonance signal at g = 2.02 is due to Fe{sup 3+} ions coupled by exchange interaction. It is interesting to observe that the number of spins participating in resonance (N) and its paramagnetic susceptibility ({chi}) exhibits the mixed alkali effect with composition. The present study also gives an indication that the size of alkali ions we choose in mixed alkali glasses is also an important contributing factor in showing the mixed alkali effect. It is observed that the variation of N with temperature obeys Boltzmann law. A linear relationship is observed between 1/{chi} and T in accordance with Curie-Weiss law. The paramagnetic Curie temperature ({theta} {sub p}) is negative for the investigated sample, which suggests that the iron ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. The optical absorption spectra exhibit only one weak band corresponding to the transition {sup 6}A{sub 1g}(S) {sup {yields}} {sup 4}A{sub 1g}(G); {sup 4}E{sub g}(G) at 446 nm which is a characteristic of Fe{sup 3+} ions in octahedral symmetry.

• OSTI ID: 20895266
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 9 Vol. 41; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION
ABSORPTION SPECTRA
AXIAL SYMMETRY
BORATES
BORON OXIDES
CURIE POINT
CURIE-WEISS LAW
ELECTRON SPIN RESONANCE
FERRITES
GLASS
IRON IONS
IRON OXIDES
LITHIUM OXIDES
PARAMAGNETISM
SIGNALS
SODIUM OXIDES