Magnetic and piezoelectric properties of the Bi$_{1-x}$La$_x$FeO$_3$ system near the transition from the polar to antipolar phase

The crystal structure, piezoelectric and magnetic properties of the Bi$_{1-x}$La$_x$FeO$_3$ solid-solution system near the structural transition between the rhombohedral and orthorhombic phases (0.15 $\le x\le$ 0.2) have been investigated. The regions of existence of the polar rhombohedral and orthorhombic phases have been determined, and the sequence of structural transitions as a function of the lanthanum ion concentration and temperature has been studied. The maximum piezoelectric signal is found for the solid solution with the composition $x$ = 0.16, which has a single-phase rhombohedral structure. The relation between the type of crystal structure distortions and the increase in the magnetization upon the concentration-driven structural transition from the polar to antipolar phase has been established.