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Large and Tunable Polar-Toroidal Coupling in Ferroelectric Composite Nanowires toward Superior Electromechanical Responses.

Chen WJ, Zheng Y, Wang B - Sci Rep (2015)

Bottom Line: Particularly, a strong polar-toroidal coupling that is tunable by the SrTiO3-layer thickness, temperature, external strains and electric fields is found to exist in the nanowires, with the appearance of fruitful dipole states (including those being purely polar, purely toroidal, both polar and toroidal, or distorted toroidal) and phase boundaries.As a consequence, an efficient cross control of the toroidal (polar) order by static (curled) electric field, and superior piezoelectric and piezotoroidal responses, can be achieved in the nanowires.The result provides new insights into the collective dipole behaviors in nanowire systems.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, China [2] Micro &Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, China.

ABSTRACT
The collective dipole behaviors in (BaTiO3)m/(SrTiO3)n composite nanowires are investigated based on the first-principles-derived simulations. It demonstrates that such nanowire systems exhibit intriguing dipole orders, due to the combining effect of the anisotropic electrostatic interaction of the nanowire, the SrTiO3-layer-modified electrostatic interaction and the multiphase ground state of BaTiO3 layer. Particularly, a strong polar-toroidal coupling that is tunable by the SrTiO3-layer thickness, temperature, external strains and electric fields is found to exist in the nanowires, with the appearance of fruitful dipole states (including those being purely polar, purely toroidal, both polar and toroidal, or distorted toroidal) and phase boundaries. As a consequence, an efficient cross control of the toroidal (polar) order by static (curled) electric field, and superior piezoelectric and piezotoroidal responses, can be achieved in the nanowires. The result provides new insights into the collective dipole behaviors in nanowire systems.

No MeSH data available.


Related in: MedlinePlus

Piezoelectric and piezotoroidal responses of the nanowires.(a) The strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature at zero external fields. (b) The calculated piezoelectric  and piezotoroidal  coefficients of (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. (c) Inverse and (d) direct piezotoroidal effect in (BaTiO3)10/(SrTiO3)2 nanowire at T = 250 K. The nanowire has an initial purely toroidal state. (c) The strain state of the nanowire as a function of a curled field EC = Saez × r. The insert depicts the strain state of BaTiO3 nanodot as a function of Sa at T = 250 K. (d) The toroidization and polarization as functions of constrained strain η33.
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f4: Piezoelectric and piezotoroidal responses of the nanowires.(a) The strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature at zero external fields. (b) The calculated piezoelectric and piezotoroidal coefficients of (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. (c) Inverse and (d) direct piezotoroidal effect in (BaTiO3)10/(SrTiO3)2 nanowire at T = 250 K. The nanowire has an initial purely toroidal state. (c) The strain state of the nanowire as a function of a curled field EC = Saez × r. The insert depicts the strain state of BaTiO3 nanodot as a function of Sa at T = 250 K. (d) The toroidization and polarization as functions of constrained strain η33.

Mentions: We now turn to the electromechanical responses of the nanowires when they are under external electric fields or strain constraint, which are related to the well known piezoelectric and the less reported piezotoroidal effects12. Figure 4a depicts the strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature under zero external fields. For each nanowire, a change of strain state is accompanied with the transition of dipole states. Particularly, a large change of axial strain happens near the phase boundary of paraelectric state and state B in the (BaTiO3)10/(SrTiO3)2 nanowire, and the phase boundary of state D and state C(E) in (BaTiO3)10/(SrTiO3)3(4) nanowire, indicating large electromechanical responses near these phase boundaries. Figure 4b depicts the calculated piezoelectric and piezotoroidal coefficients of the (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. Two remarkable observations are as follows. (1) Both nanowires have an overall notable piezoelectric coefficient (>50 pC/N) with a peak over 500 pC/N and 1200 pC/N near the phase boundary of polar and nonpolar states. (2) The piezotoroidal coefficient of the nanowires also exhibits a peak near the phase boundary of PTMO state and non-toroidal states, with an overall large value (>0.02 e/GpaǺ even near 0 K). Such an overall large is a result of polar-toroidal coupling, and is an order larger than that previously found in PZT nanodot12. Moreover, the peak value of is found comparable with BaTiO3 nanodot, which has a large at moderate temperatures due to vortex rotation (see Supplementary Figure S8c).


Large and Tunable Polar-Toroidal Coupling in Ferroelectric Composite Nanowires toward Superior Electromechanical Responses.

Chen WJ, Zheng Y, Wang B - Sci Rep (2015)

Piezoelectric and piezotoroidal responses of the nanowires.(a) The strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature at zero external fields. (b) The calculated piezoelectric  and piezotoroidal  coefficients of (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. (c) Inverse and (d) direct piezotoroidal effect in (BaTiO3)10/(SrTiO3)2 nanowire at T = 250 K. The nanowire has an initial purely toroidal state. (c) The strain state of the nanowire as a function of a curled field EC = Saez × r. The insert depicts the strain state of BaTiO3 nanodot as a function of Sa at T = 250 K. (d) The toroidization and polarization as functions of constrained strain η33.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4477413&req=5

f4: Piezoelectric and piezotoroidal responses of the nanowires.(a) The strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature at zero external fields. (b) The calculated piezoelectric and piezotoroidal coefficients of (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. (c) Inverse and (d) direct piezotoroidal effect in (BaTiO3)10/(SrTiO3)2 nanowire at T = 250 K. The nanowire has an initial purely toroidal state. (c) The strain state of the nanowire as a function of a curled field EC = Saez × r. The insert depicts the strain state of BaTiO3 nanodot as a function of Sa at T = 250 K. (d) The toroidization and polarization as functions of constrained strain η33.
Mentions: We now turn to the electromechanical responses of the nanowires when they are under external electric fields or strain constraint, which are related to the well known piezoelectric and the less reported piezotoroidal effects12. Figure 4a depicts the strain state of the (BaTiO3)10/(SrTiO3)n nanowires with n = 2, 3 and 4 as a function of temperature under zero external fields. For each nanowire, a change of strain state is accompanied with the transition of dipole states. Particularly, a large change of axial strain happens near the phase boundary of paraelectric state and state B in the (BaTiO3)10/(SrTiO3)2 nanowire, and the phase boundary of state D and state C(E) in (BaTiO3)10/(SrTiO3)3(4) nanowire, indicating large electromechanical responses near these phase boundaries. Figure 4b depicts the calculated piezoelectric and piezotoroidal coefficients of the (BaTiO3)10/(SrTiO3)2 and (BaTiO3)10/(SrTiO3)3 nanowires. Two remarkable observations are as follows. (1) Both nanowires have an overall notable piezoelectric coefficient (>50 pC/N) with a peak over 500 pC/N and 1200 pC/N near the phase boundary of polar and nonpolar states. (2) The piezotoroidal coefficient of the nanowires also exhibits a peak near the phase boundary of PTMO state and non-toroidal states, with an overall large value (>0.02 e/GpaǺ even near 0 K). Such an overall large is a result of polar-toroidal coupling, and is an order larger than that previously found in PZT nanodot12. Moreover, the peak value of is found comparable with BaTiO3 nanodot, which has a large at moderate temperatures due to vortex rotation (see Supplementary Figure S8c).

Bottom Line: Particularly, a strong polar-toroidal coupling that is tunable by the SrTiO3-layer thickness, temperature, external strains and electric fields is found to exist in the nanowires, with the appearance of fruitful dipole states (including those being purely polar, purely toroidal, both polar and toroidal, or distorted toroidal) and phase boundaries.As a consequence, an efficient cross control of the toroidal (polar) order by static (curled) electric field, and superior piezoelectric and piezotoroidal responses, can be achieved in the nanowires.The result provides new insights into the collective dipole behaviors in nanowire systems.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, China [2] Micro &Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, China.

ABSTRACT
The collective dipole behaviors in (BaTiO3)m/(SrTiO3)n composite nanowires are investigated based on the first-principles-derived simulations. It demonstrates that such nanowire systems exhibit intriguing dipole orders, due to the combining effect of the anisotropic electrostatic interaction of the nanowire, the SrTiO3-layer-modified electrostatic interaction and the multiphase ground state of BaTiO3 layer. Particularly, a strong polar-toroidal coupling that is tunable by the SrTiO3-layer thickness, temperature, external strains and electric fields is found to exist in the nanowires, with the appearance of fruitful dipole states (including those being purely polar, purely toroidal, both polar and toroidal, or distorted toroidal) and phase boundaries. As a consequence, an efficient cross control of the toroidal (polar) order by static (curled) electric field, and superior piezoelectric and piezotoroidal responses, can be achieved in the nanowires. The result provides new insights into the collective dipole behaviors in nanowire systems.

No MeSH data available.


Related in: MedlinePlus