Unusual Elastic and Mechanical Behaviors of Copper Phosphate Glasses with Different Copper Valence States

Abstract

Elastic and mechanical properties such as Young's modulus E , Poisson's ratio ν, Debye temperature θ D , Vickers hardness H v , fracture toughness K c , and fracture surface energies γ f of y CuO x ·(100− y )P 2 O 5 glasses ( y = 45, 50, 55) with different copper valence states, i.e., R (Cu + ) = Cu + /(Cu + + Cu 2+ ), at room temperature (humidity 64%) have been examined. The following features have been found: (1) the glass transition temperature (218–434°C), H v (2.7–4.4 GPa), E (50.6–78.2 GPa), and θ D (358–434 K) decrease largely with increasing R (Cu + ); (2) the mean atomic volume, K c (0.56–1.14 MPa·m 1/2 ), and γ f (1.9–11.2 J·m −2 ) tend to increase with increasing R (Cu + ); (3) 50CuO x ·50P 2 O 5 glasses with R (Cu + ) = 0.42 and 0.55 have a high resistance against crack formation in Vickers indentation tests and no crack is observed in the 45CuO x ·55P 2 O 5 glass with R (Cu + ) = 0.57 under an applied load of about 98 N. The results demonstrate that elastic and mechanical properties of y CuO x ·(100− y )P 2 O 5 glasses depend strongly on the copper valence state and the CuO x /P 2 O 5 ratio. The unusal mechanical and elastic properties of copper phosphate glasses are well explained qualitatively by considering unique oxygen coordination and bonding states of Cu + ions, i.e., lower coordination number and more covalent bonding compared with Cu 2+ ions.