Effect of R ³⁺ Ions on the Structure and Properties of Lanthanum Borate Glasses

Abstract

Glass formation in the systems (mole percent) 25La 2 O 3 · xR 2 O 3 · (75 ‐ X)B 2 O 3 (R = Al, Ga) and (25 ‐ x)La 2 O 3 · xLn 2 O 3 · 75B 2 O 3 (Ln = Gd, Er, Y) was investigated. Up to 25 mol% Al 2 O 3 or Ga 2 O 3 can be substituted for B 2 O 3 , but more than ∼ 5 mol% Ln 2 O 3 substituted for La 2 O 3 caused macro phase separation. X‐ray diffraction and infrared analysis of these glasses and their devitrified products indicate that the basic structural units are similar to (B 3 O 6 ) ∞ chains found in binary 25La 2 O 3 * 75B 2 O 3 glass. However, the BO 4 units in the (B 3 O 6 ) ∞ chains are replaced by AlO 4 or GaO 4 , units when Al 2 O 3 or GaZ O 3 is substituted for B 2 O 3 . In these systems, Al 2 O 3 , Ga 2 O 3 , and B 2 O 3 act as glass formers, whereas Ln 2 O 3 and La 2 O 3 act as network modifiers. The substitution of either R 2 O 3 or Ln 2 O 3 in the lanthanum borate system changes the separation distance between adjacent (B 3 O 6 ) ∞ chains. The effect of this structural change on the molar volume, transformation temperature, thermal expansion coefficient, and transformation‐range viscosity is discussed.