Tuning room temperature T p and MR of La 1-y (Ca y-x Sr x )MnO 3 polycrystalline ceramics by Sr doping

Polycrystalline Sr−doped La1-y(Cay-xSrx)MnO3 (LCSMO, y=3/8) ceramics with x=0, y/25, 2y/25, 3y/25, 4y/25, y/3, y/2, and 2y/3 were prepared by sol−gel methods. X-ray diffraction patterns results indicated that all the bulk samples were single phase without any impurities. The structure of the samples transformed from orthorhombic phase (space group of Pnma ) to rhombohedral phase (space group of R3c) when the Sr content (x) was equal to or greater than y/2. With the increasing of x content, the temperature coefficient of resistance (TCR) and magnetic resistance (MR) decreased gradually. However, the metal to insulator transition temperature (Tp) and the MR reached at 300.4 K and 12% at 300 K for the LCSMO (x=4y/25) sample, respectively, which meant the LCSMO material could be used as a candidate for photoelectric (uncooled bolometer or infrared detectors, etc.) or magnetic devices (uncooled magnetic sensors, etc.) at room temperature. Visibly, the results indicated that the room temperature modulation of Tp and MR was observed when the site of the Ca2+ ion was substituted by the Sr2+ ion in LCSMO (y=3/8) polycrystalline ceramics. This gave rise to the increasing size of the A−site average cationic radius and improving of the Mn4+ ion concentration through double exchange between the Mn3+ and Mn4+ ions, leading to enhance the electrical and magnetic properties of LCSMO ceramics.