Synthesis, phase diagram and magnetic properties of (1 − x)BiFeO3–xLaMnO3 Solid Solution

• Single phase (1 − x)BiFeO3–xLaMnO3 (x = 0–1) solid solution were synthesized.
• The phase transitions were investigated by tuning composition and temperature.
• Phase diagram was constructed according to the results of XRD for the first time.
• The solid solution possess polarity feature at a wide concentration of x ⩽ 0.25.
• The magnetization of solid solution can be greatly enhanced when x > 0.08.

In this paper, we report the syntheses of (1 − x)BiFeO3–xLaMnO3 solid solution (x = 0–1) by an improved sol–gel method. With careful characterization of crystal structures of the as-prepared products and the phase transition as a function of temperature, the phase diagram of (1 − x)BiFeO3–xLaMnO3 solid solution has been determined. With the increasing of x value, the crystal structure of the samples transforms from rhombohedral R3c (x ⩽ 0.13) to tetragonal P4mm (0.14 ⩽ x ⩽ 0.25), cubic Pm3¯m (0.26 ⩽ x ⩽ 0.78), and finally to rhombohedral R3¯c (0.80 ⩽ x ⩽ 1.00). In situ high temperature X-ray powder diffraction (HTXRD) studies reveal that the phase transformations of rhombohedral R3c to orthorhombic Pbnm and tetragonal P4mm to orthorhombic Pbnm occur at 600–750 °C and 580–700 °C, respectively. The phase structures of cubic Pm3¯m and rhombohedral R3¯c keep unchanged at temperature below 880 °C. However, a second-order-like phase transition was observed at higher temperature because of the change of thermo expansion coefficient. The complete phase diagram was then drawn based on those experimental results. It can be found clearly from the phase diagram that the as-prepared (1 − x)BiFeO3–xLaMnO3 (x = 0–1) solid solutions provided more options to tune the magnetism and multiferroism, as the crystal structures possess polarity feature at a wide doping concentration of LaMnO3 (x ⩽ 0.25). We then selectively studied the magnetic properties of possible multiferroic phases, i.e. R3c and P4mm phases. The results revealed that the magnetic property can be greatly enhanced when doping fraction of LaMnO3 is more than 0.08 (x > 0.08).