Sol–gel synthesis and characterization of xCuO–(1 − x)Bi2O3 (0.15 ≤ x ≤ 0.55) glasses by magnetic and spectral studies

• Compositions ensure single phase glass formation.
• Glasses are weakly ferromagnetic in nature at 300 K.
• EPR lineshapes are isotropic in the range 5–300 K.
• Hopping activation energy of Cu2 + (3d9) small polaron in the glasses is ~ 1 × 10− 4 eV.
• Optical band ~ 400 nm is attributed to 2B1g → 2Eg transitions in Cu2 +(3d9) ions.

Binary glasses having compositions xCuO–(1 − x)Bi2O3 (0.15 ≤ x ≤ 0.55) (A1–A5: x:: 0.15, 0.25, 0.35, 0.45, 0.55) are prepared by sol–gel method. Glassy phase is ascertained by powder X-ray diffraction (XRD) studies. Glass transition temperatures, Tg, of the glasses are observed to be ~ 573 K. Magnetic studies on the glasses at 300 K in the range ± 10 kG show weak ferromagnetic nature, and additionally the particular glass A3 (x = 0.35) at 5 and 300 K in the range 0–6500 Oe also indicates weak ferromagnetic nature. Observed electron paramagnetic resonance (EPR) lineshapes of the glasses in the range 5–300 K are isotropic in nature, and the corresponding giso-values ~ 2.1 ± 0.001 are due to similar site symmetries around the Cu2 +(3d9) ions. Thermally assisted hopping of Cu2 +(3d9) small polaron modulates the EPR lineshapes which results in motionally narrowed lineshapes. Activation energy of hopping, Ea, of the small polaron, calculated from derivative EPR peak-to-peak linewidths of the glasses are observed to be ~ 1 × 10− 4 eV (~ 1011 Hz). Broad optical absorption bands ~ 400 nm and ~ 660–735 nm in the glasses are attributed to 2B1g → 2Eg and 2B1g → 2B2g transitions from the ground state 2B1g (|dx2−y2 >) in Cu2 +(3d9) ions in tetragonally distorted octahedral environment.