论文标题
铁磁性宝物中电动极化的巨型热增强$ _ {1-x} $ co $ _ {x} $ o $ $ _ {3} $ solod Solutions
Giant Thermal Enhancement of the Electric Polarization in Ferrimagnetic BiFe$_{1-x}$Co$_{x}$O$_{3}$ Solid Solutions Near Room Temperature
论文作者
论文摘要
热激发通常会减少铁电材料中的电偏振。在这里，我们通过第一原则计算显示多色Bife $ _ {1-x} $ co $ _ {x} $ o $ $ $ _ {3} $固体解决方案，$ 0.25 \ le x \ le x \ le 0.50 $（bfco）代表了这种行为的例外。特别是，我们发现，在室温和中等压力下，$ 0.1 $ -1.0 $ GPA，具体取决于构图，批量BFCO的电极化增加了$ \ sim 200 $％。这种特殊行为的起源是涉及低$ t $ rhombohedral（$ {\ cal r} $）阶段的相变和高$ t $ super-tetragonal（$ {\ cal t} $）相。 $ {\ cal r} $和$ {\ cal t} $阶段都是靠近室温的铁磁性，近似于$ 0.13 $$μ__{b} $每个配方奶粉单位。与Bifeo $ _ {3} $或BICOO $ _ {3} $中发生的情况相反，$ {\ cal t} $相位通过增加较高的振动熵而在$ {\ cal r} $上稳定在$ {\ cal r} $上。这种非凡的$ t $诱导的$ {\ cal r} \ to {\ cal t} $相变的起源是涉及过渡金属和氧离子的一致位移的极性声子模式。
Thermal excitations typically reduce the electric polarization in ferroelectric materials. Here, we show by means of first-principles calculations that multiferroic BiFe$_{1-x}$Co$_{x}$O$_{3}$ solid solutions with $0.25 \le x \le 0.50$ (BFCO) represent a noteworthy exception to this behaviour. In particular, we find that at room temperature and for moderate pressures of $0.1$-$1.0$ GPa, depending on the composition, the electric polarization of bulk BFCO increases by $\sim 200$%. The origin of such an exceptional behavior is a phase transformation involving a low-$T$ rhombohedral (${\cal R}$) phase and a high-$T$ super-tetragonal (${\cal T}$) phase. Both ${\cal R}$ and ${\cal T}$ phases are ferrimagnetic near room temperature with an approximate net magnetization of $0.13$$μ_{B}$ per formula unit. Contrarily to what occurs in either bulk BiFeO$_{3}$ or BiCoO$_{3}$, the ${\cal T}$ phase is stabilized over the ${\cal R}$ by increasing temperature due to its higher vibrational entropy. This extraordinary $T$-induced ${\cal R} \to {\cal T}$ phase transition is originated by polar phonon modes involving concerted displacements of transition-metal and oxygen ions.
