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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.


Cross control of toroidal (polar) order by static (curled) electric field.Evolution of dipole states of (BaTiO3)10/(SrTiO3)2 nanowire under an external static field EH = Eaez or a curled field EC = Saez × r. The initial dipole states of the nanowire are those obtained during a cooling-down process under zero external fields. (a) The toroidization and polarization as functions of Ea at T = 50 K. (b) The toroidization as a function of Ea at different temperatures. (c) The toroidization and polarization as functions of Sa at T = 250 K. (d) The polarization as a function of Sa at different temperatures.
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f3: Cross control of toroidal (polar) order by static (curled) electric field.Evolution of dipole states of (BaTiO3)10/(SrTiO3)2 nanowire under an external static field EH = Eaez or a curled field EC = Saez × r. The initial dipole states of the nanowire are those obtained during a cooling-down process under zero external fields. (a) The toroidization and polarization as functions of Ea at T = 50 K. (b) The toroidization as a function of Ea at different temperatures. (c) The toroidization and polarization as functions of Sa at T = 250 K. (d) The polarization as a function of Sa at different temperatures.

Mentions: The sensitivity of the state stability to SrTiO3 layer thickness implies that we may achieve large tunability of the dipole states of the nanowires by applying external fields. The large tunability is evidenced by simulations on the electromechanical responses of the nanowires under external electric and mechanical fields (for more results, see Supplementary Figure S2-S7). Behavior of the (BaTiO3)10/(SrTiO3)2 nanowire under an external z-directed static electric field EH = Eaez at T = 50 K is depicted in Fig. 3a. Note that, at a given temperature, the nanowire initially adopts a dipole state that was obtained during a cooling-down process under zero external electric field (see Fig. 2b). The nanowire is thus initially in PTMO state C at T = 50 K. The important observations are following. (1) For such PTMO state with toroidal order, it would transform into a purely polar state under the action of electric field. Different from the complicated path predicted in nanoparticles29, this transformation is achieved by the simple collective tilting of dipoles to the z-axis. (2) The system’s toroidization exhibits a large and linear response at low field region (see the gray area in Fig. 3a), another remarkable feature of our system that is similar to that of BaTiO3 nanowires embedded in a SrTiO3 matrix18 and in contrast with the small and quadratic response of the nanoparticles29. Particularly, for Ea within the coercive field (~1 MV/cm), the toroidization changes linearly with Ea (either increases or decreases depending on the direction of the field versus the polarization) in a law of gz(Ea) = g0 − χEa, where g0 is the zero-field toroidization and the toroidal susceptibility of static field χ is about 2.8 e/V by a linear fitting. Beyond the coercive field, an increase of Ea monotonously increases the polarization magnitude and decreases the toroidization, with a vanishing of toroidal order at a field of about 7 MV/cm.


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

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

Cross control of toroidal (polar) order by static (curled) electric field.Evolution of dipole states of (BaTiO3)10/(SrTiO3)2 nanowire under an external static field EH = Eaez or a curled field EC = Saez × r. The initial dipole states of the nanowire are those obtained during a cooling-down process under zero external fields. (a) The toroidization and polarization as functions of Ea at T = 50 K. (b) The toroidization as a function of Ea at different temperatures. (c) The toroidization and polarization as functions of Sa at T = 250 K. (d) The polarization as a function of Sa at different temperatures.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Cross control of toroidal (polar) order by static (curled) electric field.Evolution of dipole states of (BaTiO3)10/(SrTiO3)2 nanowire under an external static field EH = Eaez or a curled field EC = Saez × r. The initial dipole states of the nanowire are those obtained during a cooling-down process under zero external fields. (a) The toroidization and polarization as functions of Ea at T = 50 K. (b) The toroidization as a function of Ea at different temperatures. (c) The toroidization and polarization as functions of Sa at T = 250 K. (d) The polarization as a function of Sa at different temperatures.
Mentions: The sensitivity of the state stability to SrTiO3 layer thickness implies that we may achieve large tunability of the dipole states of the nanowires by applying external fields. The large tunability is evidenced by simulations on the electromechanical responses of the nanowires under external electric and mechanical fields (for more results, see Supplementary Figure S2-S7). Behavior of the (BaTiO3)10/(SrTiO3)2 nanowire under an external z-directed static electric field EH = Eaez at T = 50 K is depicted in Fig. 3a. Note that, at a given temperature, the nanowire initially adopts a dipole state that was obtained during a cooling-down process under zero external electric field (see Fig. 2b). The nanowire is thus initially in PTMO state C at T = 50 K. The important observations are following. (1) For such PTMO state with toroidal order, it would transform into a purely polar state under the action of electric field. Different from the complicated path predicted in nanoparticles29, this transformation is achieved by the simple collective tilting of dipoles to the z-axis. (2) The system’s toroidization exhibits a large and linear response at low field region (see the gray area in Fig. 3a), another remarkable feature of our system that is similar to that of BaTiO3 nanowires embedded in a SrTiO3 matrix18 and in contrast with the small and quadratic response of the nanoparticles29. Particularly, for Ea within the coercive field (~1 MV/cm), the toroidization changes linearly with Ea (either increases or decreases depending on the direction of the field versus the polarization) in a law of gz(Ea) = g0 − χEa, where g0 is the zero-field toroidization and the toroidal susceptibility of static field χ is about 2.8 e/V by a linear fitting. Beyond the coercive field, an increase of Ea monotonously increases the polarization magnitude and decreases the toroidization, with a vanishing of toroidal order at a field of about 7 MV/cm.

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.