The most common such materials are lead zirconate titanate and barium titanate. Commercially used piezoceramic is primarily lead zirconate titanate (PZT). Hard and soft Lead zirconate titanate generally differ in their piezoelectric constants. Barium titanate is an inorganic compound with chemical formula BaTiO. Barium titanate is ferroelectric and its dielectric constant varies with temperature. Barium titanate crystals find use in nonlinear optics. Early piezoelectric materials used in transducers such as barium titanate had poor temperature stability. It belongs to the ABO structure ferroelectrics like lithium tantalate and barium titanate. Lafontaine graduated in 1969; his thesis concerned the production of monocrystalline barium titanate. This renders it a possible more biospherically inert alternative to barium titanate. Lithium titanate is the anode component of the fast recharging lithium-titanate battery. The BaTiO3 (barium titanate) was discovered by T. Ogawa in 1943. Dysprosium titanate was undergoing evaluation for pressurized water control rods. Dysprosium titanate, like holmium titanate and holmium stannate, is a spin ice material. The most prominent compounds with such properties are dysprosium titanate (DyTiO) and holmium titanate (HoTiO).