Structural phase separation in La2/3Ba1/3MnO3: macroscopic and microscopic aspects

The structural phase transformation in the La2/3Ba1/3MnO3 perovskite manganite was studied by ultrasound, neutron diffraction and electron microscopy techniques. Minima of the velocity and maxima of the decrement of the ultrasound point out the structural transition temperature Ts=200 K. The hysteretic temperature behavior and giant alteration of the ultrasound velocity and decrement present an evidence of martensitic character of the phase transition at a macroscopic level. The martensitic transformation in La2/3Ba1/3MnO3 is tightly connected with electronic transitions in both coexisting high symmetry R3c and low symmetry Imma crystal phases. Neutron diffraction data show that the electronic structure of the compound exhibits anomalous behavior in the vicinity of Ts: temperature dependences of the Mn-O-Mn bond angles and Mn-O bond lengths have singularities. Parameters of the coexisting crystalline phases studied have different character of temperature correlation with parameters of the magnetic subsystem of the compound.