Thermo-mechanical properties of La2NiO4+δ

Elastic and fracture behavior of La2NiO4+delta have been assessed. Fracture stress and elastic modulus of porous La2NiO4+delta were evaluated from room temperature (RT) up to 900 A degrees C on the basis of 4-point bending tests. Both parameters increase slightly from RT to 700 A degrees C. However, at higher temperatures the elastic modulus decreases, whereas the fracture stress increases. In addition, elastic modulus and damping/internal friction of dense specimens were measured by a resonance method. A strong change of elastic modulus and internal friction between RT and 100 A degrees C appears to be related to an orthorhombic-tetragonal phase transition. No indications of phase transition can be observed at higher temperatures. Although thermogravimetric measurements suggest that oxygen was continuously released from the lattice up to 1000 A degrees C with increasing temperature, the thermal expansion coefficient showed a rather stable value from RT up to 1000 A degrees C.