Synthesis and structure–property relations in xMoO3–0.6B2O3–(0.4−x)K2O (0.010 ≤ x ≤ 0.295) glasses

• Compositions ensure single phase glass formation.
• Glasses are soft ferromagnetic in nature at 300 K.
• Paramagnetic sites in the glasses are molybdenyl MoO3 + ions.
• Mo5 +(4d1) small polaron exchange integrals at 300 K are ~ 0.052 eV in the glasses.
• Broad band ~ 750 nm in glass G4 is due to 2B2g → 2B1g transitions in Mo5 +(4d1) ions.

Glasses having compositions xMoO3–0.6B2O3–(0.4x)K2O (0.010 ≤ x ≤ 0.295)(G1–G4: x :: 0.01, 0.105, 0.200, 0.295) are prepared by sol–gel method. Powder X-ray diffraction (XRD) patterns ensure clean glassy phase in the samples. Glass transition temperature, Tg, is found to be ~ 609–625 K in the glasses. IR spectroscopic results show the presence of trigonal [BO3/2], tetrahedral [BO4/2]−, octahedral [OMoO5//2]2 −, and trigonal [BOn+(3−n)/2]n−(n = 1, 2, 3) units with free oxygens in the glasses. The glasses exhibit hysteresis loops at 300 K with fairly low values of loop areas and coercivities which indicate soft ferromagnetic nature of the glasses. Calculated values of the Mo5 +(4d1) small polaron exchange integrals from the obtained Weiss constant at 300 K are found to be ~ 0.052 eV in the glasses. Observed electron paramagnetic resonance (EPR) lineshapes at 7, 105 and 300 K are isotropic in nature in general. The observed giso-values ~ 1.90 ± 0.001–1.93 ± 0.001 indicate that the paramagnetic molybdenyl, MoO3 +(4d1), ions are in octahedral coordination with tetragonal distortion. Optical absorption broad band ~ 238–311 nm is due to charge transfer phenomenon and the broad and weak band ~ 750 nm in the glass G4 is due to the 2B2g (∣ dxy > → 2B1g (∣ dx2 − y2 >) transitions in Mo5 +(4d1) ions in distorted octahedral coordination.