Cerium forms a stoichiometric dioxide, CeO, where cerium has an oxidation state of +4. Monazite is an important ore for thorium, lanthanum, and cerium. Lanthanum usually occurs together with cerium and the other rare earth elements. Mesoporous oxides of niobium, tantalum, titanium, zirconium, cerium and tin have also been reported. It is always preceded by cerium, lanthanum and usually also by neodymium. This row would begin with a trivalent lanthanum, a teravalent cerium, and a pentavalent didymium. Cerium(IV) oxide is formed by the calcination of cerium oxalate or cerium hydroxide. Zirconium, cerium, and calcium increase toughness by controlling the shape of inclusions. These contain other toxic metals, such as chromium, vanadium and cerium. They replaced the commonly used YSZ electrolyte with a CGO (cerium gadolinium oxide) electrolyte. Berzelius is credited with identifying the chemical elements silicon, selenium, thorium, and cerium. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. This effect is suppressed by addition of cerium oxide. The original proposed refrigerant was a paramagnetic salt, such as cerium magnesium nitrate. It also developed methods of preparing and casting thorium, cerium and beryllium.