Solid solution LaCr1-xMgxO3, 0 < x <= 0.25 was prepared by heating stoichiometric amounts of appropriate oxides in air at 1400 degrees C, 48 h. At room temperature it crystallizes in orthorhombically distorted GdFeO3-type structure (a approximate to root 2 x a(per); b approximate to root 2 x a(per); c approximate to 2 x a(per), where a(per) - perovskite subcell parameter). High-temperature X-ray powder diffraction (HT XRPD) and dilatometry revealed first order phase transition to rhombohedral perovskite phase (R-3c, a approximate to root 2 x a(per), c approximate to 2 root 3 x a(per)) at 260-311 degrees C (OR phase transition). Crystal structures of room-temperature orthorhombic and high-temperature rhombohedral phases for LaCr0.75Mg0.25O3 were refined using HT XRPD data. Temperature of OR phase transition increases gradually with increasing of magnesium content. Low-temperature orthorhombic phase exhibits TEC lower in comparison with high-temperature rhombohedral one (e.g. for LaCr0.85Mg0.15O3 TEC(O) = 8.8 ppm K-1; TEC(R) = 11.6 ppm K-1). TEC for rhombohedral phase increases with increasing magnesium content from 10.4 ppm K-1 for LaCr0.95Mg0.05O3 to 12.1 ppm K-1 for LaCr0.75Mg0.25O3. (C) 2012 Elsevier Ltd. All rights reserved.