LaMnO3

LaMnO3 is an oxide of lanthanum and manganese with the chemical formula LaMnO3. It is the undoped parent compound of the manganite family and is widely studied as a model system for strongly correlated electron behavior in transition-metal oxides. At room temperature it adopts a distorted perovskite structure, typically orthorhombic with Pnma symmetry, a distortion driven by cooperative Jahn-Teller effects on MnO6 octahedra and tilting of the Mn-O framework.

The manganese in LaMnO3 is predominantly Mn3+, which has a high-spin d4 configuration. This electronic arrangement promotes Jahn-Teller distortions and cooperative orbital ordering, leading to an insulating and magnetically ordered state. The material is a Mott-type insulator and exhibits antiferromagnetic order at low temperature, with an A-type antiferromagnetic structure and a Néel temperature around 140 K.

Doping and defects strongly modify its properties. Substituting trivalent lanthanum with divalent ions such as Sr2+ or Ca2+ introduces Mn4+ and suppresses the orbital order, often driving the system toward a ferromagnetic metallic state in many compositions. This change underlies the colossal magnetoresistance observed in doped manganites near certain doping levels. Oxygen nonstoichiometry, expressed as LaMnO3+δ, also affects the structure and electronic behavior.

Synthesis typically involves solid-state methods at high temperatures, with careful control of oxygen content. LaMnO3 serves as a benchmark material for studying Jahn-Teller distortions, orbital ordering, and the interplay between lattice, charge, and spin in correlated oxide systems.