Mixed‐Alkali Effect in Low‐Alkali Germanate Glasses

Direct‐current conductivities of mixed‐alkali Na 2 O‐K 2 O‐GeO 2 glasses with ∼0.02 mol% total alkali were investigated. No minima in conductivity isotherms were indicated as K 2 O is substituted for Na 2 O. However, a conductivity‐suppressing effect with the‐addition of K 2 O to Na 2 0‐GeO 2 glass was demonstrated, from the comparison with the conductivity ofNa 2 O‐GeO 2 glasses of varied sodium content (0.0079∼0.30 mol% Na 2 O.