Transport and magnetic properties of a Mott-Hubbard system whose bandwidth and band filling are both controllable

Transport and magnetic properties of (Formula presented) have been systematically investigated varying the one-electron bandwidth (Formula presented) and the band filling (Formula presented) which can be controlled by the (Formula presented)-dependent lattice distortion and by the Ca content (Formula presented) and/or oxygen offstoichiometry (Formula presented) respectively. The end compound (Formula presented) is a (Formula presented) Mott-Hubbard insulator and its charge-gap magnitude increases with decreasing ionic radius of (Formula presented) i.e., an increase of electron correlation (Formula presented) in proportion with (Formula presented) where (Formula presented) is the critical value for the (hypothetical) (Formula presented) Mott transition. Such a Mott insulator is transformed to a correlated metal by substitution of (Formula presented) with Ca (hole doping), and the nominal hole concentration required for the insulator-metal transition (Formula presented) increases in proportion with (Formula presented) Concerning magnetism, (Formula presented) with (Formula presented) Pr, Nd, and Sm, shows the antiferromagnetic ordering and its Néel temperature (Formula presented) decreases with smaller (Formula presented) also decreases with Ca doping, but remains finite up to the metal-insulator phase boundary. On the basis of these results, electronic phase diagrams are derived for a series of titanates as an electron-correlated system with changes of two parameters, i.e., the strength of electron correlation and band filling. Possible origins of the insulating state with finite hole doping are also discussed in terms of the kinetic energy of doped carriers in the Mott-Hubbard insulator.