Abnormal ferroelectric response and enhancement of piezoelectricity of PbTiO3 under uniaxial compression

The ferroelectricity of rhombohedral PbTiO3 under uniaxial compression is investigated from first-principles study. Upon compression, the ferroelectricity decreases until a critical stress of -29 GPa and then increases with a further increase of the magnitude of the uniaxial compressive stress. We also find that uniaxial compression could enhance piezoelectricity and that the maximum piezoelectric coefficient d(33) occurs at sigma(33)=-49 GPa, which supports the experimentally observed piezoelectric behavior in rhombohedral Pb(Mg1/3Nb2/3O3)-0.32PbTiO(3) [Q. Wan, C. Chen, and Y. P. Shen, J. Appl. Phys. 98, 024103 (2005)]. Our calculated results show that the Pb, Ti, and O atoms have different contributions to the total polarization with increasing the magnitude of uniaxial compressive stress, and that when -sigma(33)>55 GPa, the Ti atoms no longer have contributions to the polarization, which leads to the changes of ferroelectricity and piezoelectricity. (C) 2008 American Institute of Physics.

Studies of tetragonal PbTiO3 subjected to uniaxial stress along the c-axis

Tetragonal PbTiO3 under uniaxial stress along the c-axis is investigated from first-principles. The structural parameters, polarization, and squares of the lowest optical phonon frequencies for E(1TO) and A(1)(1TO) modes at Gamma show abrupt changes near a stress sigma(c) of 1.04 GPa, which is related to the dramatic change of elastic constant c(33) resulting from the uniaxial stress applied along the c-axis. We also find that the uniaxial compressive stress could enhance the piezoelectric stress coefficients, whereas the uniaxial tensile stress could enhance the piezoelectric strain coefficients. It is also found that when the magnitude of uniaxial compressive stress sigma(33) is greater than 12 GPa, PbTiO3 is transformed to the paraelectric tetragonal phase.

具有表面光电特性的PbTiO_3纳米晶的尺寸效应

利用溶胶-凝胶法制备不同粒径的PbTiO3纳米晶．表面光电压谱的研究结果表明，随粒径尺寸的减小，其表面光伏响应发生谱带加宽现象，并出现新的体相跃迁光伏响应结构．这些特性是小尺寸PbTiO3纳米晶内不同于体相PbTiO3的Ti4+的d轨道配位环境的体现.

外电场对PbTiO_3纳米晶表面光电特性的影响

研究了1000℃（1#）和450℃（2#）条件下烧结的PbTiO纳米晶，在外电场处理前后的表面光电特性．结果表明，外电场的处理对PbTiO3纳米晶表面光电特性的影响具有明显的尺寸效应：经外电场处理后1#PbTiO3纳米晶表面光优响应没有变化；2#PbTiO3纳米晶变化明显