The multiferroic material Bi1-xSmxFeO3 shows ferroelectric and antiferromagnetic properties in
the ground state of the Bi-rich side. When the Sm content increases from
x = 0 in BiFeO3, the (ferroelectric-R3c
→ paraelectric-Pnma) state change occurs around x
= 0.14. According to the previous studies on
Bi1-xSmxFeO3, the state boundary between the R3c and Pnma states can be
identified as a morphotropic phase boundary (MPB), which is nearly parallel to
the temperature axis in the state diagram. The notable feature of
Bi1-xSmxFeO3 is that a remarkable piezoelectric response was also found
near the MPB. However, the origin of the remarkable response has not been
understood sufficiently. In this study, thus, the crystallographic features in
the vicinity of the MPB have been examined by x-ray powder diffraction and
transmission electron microscopy. It was confirmed that the R3c and Pnma states
were present for 0 ≤ x ≤ 0.15 and for
0.16 ≤ x ≤ 0.30, respectively. In
addition to these states, there also existed the PbZrO3-type state
around x = 0.15, which was identified as a modulated
structure. Based on the analysis of the modulated structure, furthermore, it was
suggested that the PbZrO3-type state could be regarded as a 2q state,
which is characterized by two transverse modulation waves with k1
= [1/2 0 0]o and k2 = [0 1/2
0]o in the orthorhombic-Pnma notation.