We employ first-principles calculations to study the magnetic and ferroelectric properties of PbVO 3 with A (X A = Ca, Sr, Bi, Ba, and La) or B (X B = Ti, Cr, Mn, Fe, Co, Ni, and Cu) site dopants, with the aim of ascertaining a large ferroelectric polarization and a long magnetic order, or even a macro ferri/ferromagnetism, which is critical to their potential applications in magnetoelectronic devices. It is found that Pb 7 X A V 8 O24 (X A = Ca, Sr, and Ba,) are inclined to maintain the spin glass and large ferroelectric polarization. The degenerated G- and C-antiferromagnetic (AFM) couplings in the ideal PbVO 3 are broken up, accompanied by the loss of ferroelectric properties, when La or Bi is doped at the A site. In contrast, the above-mentioned 3d transition elements doped at the B site of PbVO 3 could induce remnant magnetic moments and preserve the large ferroelectric polarization, except for Ni and Cu. The Fe or Cr at the B site clearly remove the degenerated G- and C-AFM coupling, but the nonmagnetic Ti cannot do so. For the Mn, Co, Ni, or Cu doped at the B sites, even the two-dimensional AFM ordering in PbVO 3 is destabilized. The various doping effects are further discussed with inner strain and charge transfer.
采用基于第一性原理的赝势平面波方法,对Bi Ti O3的多种结构进行了计算.计算结果表明,C1C1结构最为稳定,对应晶格参数为a=b=5.606,c=9.954;α=β=105.1°,γ=61.2°.进一步对C1C1结构的Bi Ti O3的能带结构、电子性质和光学性质进行了研究,发现Bi Ti O3是间接带隙半导体,其费米面附近的能带主要由Ti-3d和O-2p层的电子态构成.通过介电函数、复折射率和反射率等的研究,发现Bi Ti O3的光学性质为近各向同性.
用溶胶凝胶法制备了BiFe1-x Mn x O3(0≤x≤0.3)系列粉晶样品,并研究了Mn掺杂对其结构和磁性的影响.XRD和拉曼光谱分析表明Mn掺杂使BiFeO3的晶体结构和振动模式发生了变化.Rietveld精修结果显示,在掺杂量x=0.1附近,BiFeO3的晶体结构从菱方R3c相转变为正交Pbnm相.对样品的磁性测量表明,随着Mn掺杂量的增加,样品的剩余磁化强度逐渐增大,在相变点附近达到最大值.这种磁性的变化与Mn掺杂导致的晶体结构变化有很强的关联,表明Dzyaloshinskii-Moriya相互作用是BiFe1-x Mn x O3磁性增强的主要原因.
