Sodium ions in 25NaO(1/2)-6LaO(3/2)-6GeO(2)-63PO(5/2) (mol%) glasses were substituted with protons using corona discharge treatment (CDT) under a H-2 atmosphere. The substitution of sodium ion to proton proceeded from the anode side to the cathode side with con degrees stant current flow during the CDT. A crystalline free and transparent glass plate of 0.3 mm thickness was obtained after CDT for 96 h. The maximum decrease rate from sodium ion to proton was 78 +/- 10%. The proton conductivity of 8.5 x 10(-4) S/cm was attained at 400C. (C) 2017 Elsevier B.V. All rights reserved.