Reorientation of magnetic dipoles at the antiferroelectric-paraelectric phase transition of Bi 1-x Nd x FeO 3 (0.15≤x≤0.25)

摘要: Ceramic ${\text{Bi}}_{1\ensuremath{-}x}{\text{Nd}}_{x}{\text{FeO}}_{3}$ solid solutions in the approximate compositional range $0.15\ensuremath{\le}x\ensuremath{\le}0.25$ undergo first-order antiferroelectric $(\text{AFE})\ensuremath{\leftrightarrow}\text{paraelectric}$ (PE) phase transitions between $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and room temperature. The orthorhombic AFE ($Pnam$, $\ensuremath{\surd}2{a}_{\text{c}}\ifmmode\times\else\texttimes\fi{}2\ensuremath{\surd}2{a}_{\text{c}}\ifmmode\times\else\texttimes\fi{}4{a}_{\text{c}}$, where ${a}_{\text{c}}\ensuremath{\approx}4\text{ }\text{\AA{}}$ is lattice parameter of an ideal cubic perovskite) PE ($Pbnm$, $\ensuremath{\surd}2{a}_{\text{c}}\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}2{a}_{\text{c}}\ifmmode\times\else\texttimes\fi{}2{a}_{\text{c}}$) structures differ not only type octahedral tilt system but also pattern $A$-cation (Bi/Nd) displacements. $\text{AFE}\ensuremath{\leftrightarrow}\text{PE}$ transition accompanied by a large $(\ensuremath{\approx}2\mathrm{%})$ discontinuous volume change similar to that observed at ferroelectric $(\text{FE})\ensuremath{\leftrightarrow}\text{PE}$ ${\text{BiFeO}}_{3}$. For all compositions, structural occurs within $G$-type antiferromagnetic (AFM) state. Variable-temperature magnetic measurements reveal strong coupling ordering. Rietveld refinements using neutron powder-diffraction data demonstrate reorientation dipoles AFM array resulting significant increase magnetization.