Influence of valence state of copper ions on structural and spectroscopic properties of multi-component PbO–Al2O3–TeO2–GeO2–SiO2 glass ceramic system- a possible material for memory switching devices.

Multi-component glass ceramics with composition 29PbO–5Al 2 O 3 –1TeO 2 –10GeO 2 – (55–x) SiO 2 doped with different concentrations of CuO (0 ≤ x ≤ 1.0 mol %) were synthesized by melt quenching technique and subsequent heat treatment. These glass ceramics were characterized by X–ray diffraction, scanning electron microscope, differential thermal analysis, optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman studies. The absorption spectra of these glass ceramics exhibited a broad absorption band in the range 650–950 nm which is ascribed to 2 B 1g → 2 B 2g octahedral transition of Cu 2+ ions. A feeble band around 364 nm is also identified in the samples doped with CuO up to 0.6 mol% as being due to charge transfer between the two oxidation states Cu 2+ and Cu + of copper ions. The EPR spectrum recorded at room temperature exhibited a strong resonance signal at g ⊥ = 2.072 and a shallow quadruplet at about g ǁ = 2.401. FTIR and Raman spectra of the titled samples provide significant information about various structural units viz ., silicate, germanate, PbO 4 , PbO 6 , AlO 6 , TeO 4 and TeO 3 that are present in these ceramic matrix. Analysis of the spectroscopic investigations reveals that with an increase in the concentration of CuO up to 0.6 mol% copper ions do exist in Cu 2+ and Cu + states and they act as modifiers and net work formers respectively. Therefore, glass ceramic sample contains 0.6 mol% of CuO is favorable for memory switching action. [ABSTRACT FROM AUTHOR]