text: Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped bismuth titanate ( - BLT).
  Lanthanum oxide is used in optical materials; often the optical glasses are doped with  to improve the glass' refractive index, chemical durability, and mechanical strength.
  The addition of the  to the glass melt leads to a higher glass transition temperature from 658 °C to 679 °C. The addition also leads to a higher density, microhardness, and refractive index of the glass.