The crystal structure and electrical properties of K₂NiF₄-type (Ca_2−xSm_x)MnO₄

Graphical abstract: The relationship between log ρ of K₂NiF₄-type (Ca_2−xSm_x)MnO₄ and 1000/T. - Highlights: • K₂NiF₄-type (Ca_2−xSm_x)MnO₄ was synthesized using a polymerized complex route. • The semiconductive samples had minimum values of ρ and E_a at x = 0.1. • The log ρ–1/T curve of x = 0.3 consisted of two different lines at 315 K. • The 1/χ − T curve of x = 0.3 had a peak at 325 K. • These results indicated the presence of a charge-ordering transition at x = 0.3. - Abstract: K₂NiF₄-type (Ca_2−xSm_x)MnO₄ (0.02 ≤ x ≤ 0.3) was synthesized using a polymerized complex route. The crystal structure changed from tetragonal to orthorhombic at x = 0.3. A variation in the lattice parameters was explained by the Mn–O(2) distance, the Mn−O(2)−Mn angle, and the (Ca,Sm)–(Ca,Sm) distance. The samples were n-type semiconductors, and the minimum values of electrical resistivity (ρ) and an energy gap (E_g) at x = 0.1 were accounted by electron transfer through an Mn−O(2)−Mn path and overlap between the Mnt_2g and Op_π orbitals. In the sample (x = 0.3), the log ρ–1000/T curve consisted of two different lines that intersected at ca. 325 K, and a peak was observed at ca. 315 K in the magnetic susceptibility–temperature curve. These results indicated the presence of a charge-ordering (CO) transition at 315–325 K