School of Materials Science and Technology, Institute of Technology, Banaras Hindu University
○Satendra Pal Singh Akhilesh Kumar Singh Dhananjai Pandey

Lead iron niobate Pb(Fe_1/2Nb_1/2)O₃ (PFN) is a magnetoelectric material exhibiting paraelectric to ferroelectric and a paramagnetic to antiferromagnetic phase transitions at 385K and 143K, respectively. Further, the solid solution of PFN with PbTiO_3, i.e.(1-x)[Pb(Fe_1/2Nb_1/2)O₃]-xPbTiO₃ (PFN-xPT), exhibits a morphotropic phase transition similar to that in the well known piezoelectric ceramics like Pb(Zr_xTi_1-x)O₃ (PZT), and (1-x)[Pb(Mg_1/3Nb_2/3)O₃]-xPbTiO₃ (PMN-xPT).The morphotropic phase transition is of special technological interest since the dielectric and piezoelectric responses are known to be maximized near the morphotropic phase boundary (MPB) composition. The MPB has in the past been believed to separate the tetragonal and rhombohedral phase fields. Recently, it has been shown that the tetragonal and rhombohedral phase fields are separated by a thin region of stability of one monoclinic phase (M_A) in the MPB region of PZT and two (M_B and M_C) in the PMN-xPT ceramics. In the Present work, we have synthesized pyrochlore phase free PFN-xPT ceramics and studied their structure by powder x-ray diffraction. Rietveld analysis of the powder x-ray diffraction data shows that the MPB in PFN-xPT ceramics lies around x = 0.06. Our study provides the first experimental evidence for a morphotropic phase transition from a monoclinic phase of M_A type with Cm space group to a tetragonal phase with P4mm space group in the PFN-xPT system. It is proposed that this monoclinic phase persists in the entire composition range x < 0.06, as evidenced by the presence of anomalous broadening of the 200 profile.
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