Proceedings of the

2010 IEEE International Symposium on

the Applications of Ferroelectrics

(ISAF)

9th - 12th

August 2010

Edinburgh Conference Centre,

Edinburgh, Scotland, UK

Co-located with the 10th European Conference on the Applications of Polar Dielectrics (ECAPD)

IEEE Catalog Number: CFP10ISA-ART

ISBN: 978-1-4244-8191-0

ISSN: 1099-4734

Copyright

Proceedings of the 2010 IEEE International Symposium on the Applications of Ferroelectrics (ISAF)

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IEEE Catalog Number: CFP10ISA-ART

ISBN: 978-1-4244-8191-0

ISSN: 1099-4734

Proceedings of the

2010 IEEE International Symposium on the Applications of

Ferroelectrics (ISAF)

Paper

Number

Contents

A2 Description of the nonlinear dielectric properties of ferroelectrics under a weak AC-field C. Borderon, R. Renoud and H W Gundel

A3 Theory of Unidirectional Bulk Conduction under Trap Density Gradient for Resistance Switching Yuldo Watanabe

A5 Theoretical Aspect on Relaxor Appearance in Mixed Perovskite-Oxides Eiko Matsushita

A8 Electronic Reconstruction and Transport Properties in SrTi03/SrI_xLaxTi03 Superlattice P. V Ong and Jaichan Lee

A12 The stress-assisted enhancement of piezoelectric properties due to mechanically incompatible domain structures in BaTi03 Tomas Sluka, Dragan Damjanovic, Alexander Tagantsev, Enrico Colla, Mahamudu Mtebwa and Nava Setter

A13 Polarization Dynamics and Non-Equilibrium Processes in Ferroelectric Switching Melvin M Vopson, Paul M Weaver, Markys G. Cain, Mike J Reece and KB. Chong

B8 Piezoresponse Force Microscopy study of a single-crystal LiTa03 thin film obtained by the Smart Cut™ technology Brugere A., Moulet Js., Gidon s., Tchelnokov A., Moulet Js., Ghyselen B. Deguet c., Clavelier L. and Gautier B.

E6 Proton Conductivity Measurement of the Sol-Gel Derived Yttrium-doped SrZr03 Thin Films for Fuel-Cell Applications Yuri Isse, Takashi, Nishida, Kiyoshi Uchiyama and Yukiharu Uraoka

E7 Measurement and modelisation of dielectric properties of ferroelectrics thin layers R. Renoud, C. Borderon and H W Gundel

E12 Phase optimisation of PMN-PT thin films deposited by Pulsed Laser Deposition on MgO substrates and Pt-coated Silicon Kim-Anh Bui-Thi, Philippe Lecoeur, Mai Pham-Thi and Guy Garry

F2 Influence of the thickness on structural, magnetic and electrical properties of BiFe03-PbTi03 thin film prepared by Pulsed Laser Deposition Faye Bygrave, Tim P Comyn and Andrew J Bell

H3 Preparation and Characterization of P(VDF -TrFE)/ Ah03 nanocomposite Rachid Haji, Van Son Nguyen, Brice Vincent, Didier Rouxel and Franr;ois Bauer

H5 P(VDF -TrFE)/ Ah03 piezoelectric nanocomposite thin films Van Son Nguyen, Rachid Hadji, Brice Vincent, Didier Rouxel, Frederic Sarry and Franr;ois Bauer

H9 Novel Approach for Fabrication of Ceramic Matrix Piezocomposites Andrey N Rybyanets

H12 Losses and Dispersion in Ceramic Piezocompozites Andrey N Rybyanets and Anastasia A. Rybyanets

K6 Dielectric Properties of (B�.8-xBio.2)(ZnO.l Tio.9)03 Ceramics for High Temperature Applications Natthaphon Raengthon and David P. Cann

K12 Broadband Micro-Brillouin Scattering Study of O.7Pb(Sc1l2Nbll2)03 - 0.3PbTi03 Crystals A. A. Bokov, Z-G. Ye, S. Kojima, S. Tsukada and Y Hidaka

Ll Dielectric and Multiferroic Properties of (Bi,La)Fe03 - PbTi03 Ceramics J G. Chen, L. Y Feng, G. Y Shi, L. Zhao, S. W Yu and JR. Cheng

L5 Synthesis of platelets BisFeo.sCoo.s ThOIs via the molten salt method Meghdad Palizdar , Timothy Comyn, Santosh Kulkarni, Lynette Keeney, Saibal Roy , Martyn Pemble , Roger Whatmore and Andrew J Bell

M3 Fabrication and characterizations of Multiferroic super-lattice thin films BaTi03 IBaFe03 H Yokota, H Tabata, R. Fukatani, S. Ogura, Y Uesu and G. B-Lee

M4 Multi-ferroicity of thin-film-stabilized hexagonal YbFe03 Y Uesu, H Iida, T Koizumi, K Kohn, S. Mori, R. Haumont, N Ikeda and JM Kiat

N 1 0 Determination of the Reduced Matrix of the Piezoelectric, Dielectric and Elastic Material Constants for a Piezoelectric Material with Coo Symmetry S. Sherrit, A.J Masys, HD. Wiederick and B.K Mukherjee

N15 Electromechanical Properties of PMN-PT and PZT Ceramics at Cryogenic Temperatures Mickael Thiercelin, Hichem Dammak and Mai Pham Thi

N18 Dome Bilayer PiezoelectriclElectrostrictive (PIE) Composite Flextensional Actuator Piyalak Ngernchuklin and Ahmad Safari

N19 Porous Piezoelectric Ceramics - A Historical Overview Andrey N Rybyanets

PI Dielectric and Ferroelectric Properties of BNT-Based Thin Films by Pulsed Laser Deposition Mehdi Hejazi and Ahmad Safari

P20 Vibration Velocities under High-Power Driving on Perovskite-Type Lead-Free Ferroelectric Ceramics Hajime Nagata, Koudai Takai, Yoji Nomura, Shigeki Sato, Yuji Hiruma and T Takenaka

P24 Dielectric and Piezoelectric Properties in theLead-free System Nao.sKo.sNb03 -LiTa03 -BiSc03 Fang Yuan Zhu, Steven J Milne, Tim P. Comyn and Andrew. J Bell

Q3 Analysis of noise transmission through the window glass plate and its control using the Macro Fiber Composite Actuator K Nowikowi, P. Mokry, J Vaclavik, and V Ledl

Rl Pyroelectric coefficient under open circuit condition and its enhancement through product property M J Hockley, H H .S. Chang and Z. Huang

T2 Microstructural and Electromechanical Comparison of Different Piezoelectric PZT Based Single Fibers and Their 1-3 Composites FJ Clemens, J Heiber, T Graule, M Piechowiak, L. Kozielski and D. Czekaj

T12 PFM Investigation of Stress Induced Ferroelastic Switching in Piezoelectric Bulk Ceramics Mahamudu Mtebwa, Enrico Colla, Tomas Sluka, Lars Gjl?Jdvad, Dragan Damjanovic and Nava Setter

PR12 Flux Growth and Characterisation of Rhombohedral BiFe03-PbTi03 Single Crystals C G. Cambridge, T P. Comyn, M Palizdar and A.J Bell

PR33 Crystal structure analysis of manganese and gallium doped hexagonal BaTi03 by synchrotron radiation powder diffraction

PR34

PR38

PR41

PR77

PR79

PR96

PR138

PR139

PR151

PR158

PR162

PR167

PR168

PR169

Hidesada Natsui, Osamu Odawara, Jianding Yu, Shinichi Yoda, Chikako Moriyoshi, Fumiko Yoshida and Yoshihiro

Kuroiwa

Effect of different templates on reactive template grain growth of BiFe03 -PbTi03 Meghdad Palizdar, Tim P Comyn and Andrew J Bell

Intragrain Compositional Gradient Barium Strontium Titanate Ceramics Fabricated by a Sol-assisted Sintering Technology Tingting Wang, Dengren Jin, Jinrong Cheng and Juan Li

Electrical Properties of 0-3 Piezocomposites with Thermoplastic Elastomer and Epoxy Matrix Sedat Alkoy & Mehmet Yasin Dogan

Ternary Perovskite Thin Films For Energy Harvesting MEMS Kiyotaka Wasa, Isaku Kanno, and Hidetoshi Kotera

The Dependence of Optical Properties on Composition in BFO-PT Thin Films Xiaowen Zhou, Shengwen Yu and Jinrong Cheng

Synthesis and photocatalytic property of Ba-doped BiFe03 nanoparticles Jianmin Li, Dengrong Cai, Juyue Song, Dengren Jin, Shengwen Yu, and Jinrong Cheng*

The study of BST buffered BiFe03 thin film Dong Hong, Shengwen Yu and Jinrong Cheng

Effects of Lao.sSro.sCo03 Buffer Layers on the structure and Properties of Pb(Zro.s3 Tio.47)03-CoFe204 Composite Films Xufang Yu, ShengwenYu and Jinrong Cheng

Dielectric tunability in (i-x )[Pb(Mg1l3Nb2/3)03]-x PbTi03 ceramics for tunable devices application C A. Guarany, J D. S. Guerra, E. B. Araujo and E. C Lima

The influence of mechanical stress on piezoceramic tubes R. W C Lewis, A.J Merrick, A.CE. Dent and CR. Bowen

Complex Material Constants for PZTIPZT Ceramic Composites Andrey N Rybyanets, Tamara V Domashenkina and Anastasia A. Rybyanets

Fabrication and Characterization of Ti Modified BiFe03-PbTi03 High Temperature Piezoelectric Ceramics Long Zhao, Guiyang Shi, Jianguo Chen, Shengwen Yu and Jinrong Cheng

Piezoelectric Properties of Modified (Ko.sNaO.s)Nb03-BaTi03 Ceramics with the Mixture Sintering Aids of O.6B203-O.4CuO Masatoshi Adachi, Kang Yan, Kohei Matsumoto, and Tomoaki Karaki

Effect of Cu and Li Addition on the Electrical Properties of KNN Ceramics Ebru Mensur Alkoy and Ayse Berksoy

PRI 80

PRI 8I

PRI 82

PRI 82

PRI 89

PR227

PR238

PR24I

Piezoelectric Energy Harvesting Using Lead-free (Ko.sN8{).s)O.97(Nbo.96Sbo.04)03 Ceramics Jinhee Kang, Jungrae Noh, Youngkwang Oh, Larkhoon Hwang and Juhyun Yoo

Effect of�CuNbs 023 and La203 co-doping on the Piezoelectric and Dielectric Properties of (Ko.sN8{).s)O.97 (NbO.96Sbo.04)03 Ceramics Yeongho Jeong , Jaeil Hong, Byeong-Ho Seo, Young Kwang Oh, Juhyun Yoo and Larkhoon Hwang

Dielectric and piezoelectric properties of (Ko.sN8{).s)O.97 (NbO.97Sbo.03)03 ceramics according to the K2CuNbs023 addition Shang-Ho Lee , Kab-Soo Lee, Byeong-Ho Seo, Yeong-Ho Jeong , Hyun-Sang Yoon, Ju-Hyun Yoo and Durk-Won Park

Dielectric and Piezoelectric Properties of (Ko.sN8{).s)O.97 (NbO.96Sbo.04)03 Ceramics according to the Amount of Ce02 Addition Youngkwang 0, Byungho Seo , Sangho Lee, Durkwon Park, Insung Kim, Jaesung Song and Juhyun Yoo

A system for the vibration suppression in the broad frequency range using a single piezoelectric actuator shunted by a negative capacitor M Kodejska, J Vaclavik, and P. Mokry

Planar Domain Structures Formed By Electron-Beam Poling In Y- And X-Cut LiNb03 and Waveguides Zn:LiNb03 S.M Shandarov, M V Borodin, V V Shcherbina, L. S Kokhanchik, L. Ya. Serebrennikov, Nl Burimov, A. Yu. Pechenkin, D.o. Anisimov, SA. Kuznetsova and V V Kozik

LiNb03 Polymer Composite Thin Film: Towards its Preparation Ahmad Mukifza Harun, Gareth M Vaughn, A.P. Brown, T P. Comyn and A.J Bell

Towards the Development of Efficient Low Frequency Piezoelectric Energy Harvesters Rahul Shukla, S. Adam Qaisar and Andrew J Bell

Electronic Reconstruction and Transport Properties in SrTiO3/Sr1-xLaxTiO3 Superlattice

P. V. Ong and Jaichan Lee School of Materials Science & Engineering

Sungkyunkwan University Suwon, 440-746 opvu@skku.edu

Abstract—First-principles calculation was used to study the electronic structure and transport properties of SrTiO3/Sr1-

xLaxTiO3 superlattice. We found that in comparison with bulk Sr1-xLaxTiO3 electronic structure of the superlattice is dramatically changed and strongly depends on the SrTiO3 thickness. This electronic reconstruction induces multi-type carriers which exhibit different transport characteristics. The possible functional enhancement is demonstrated.

Oxide heterostructure; two-dimensional electron gas; first-princples; electronic structure, effective mass

I. INTRODUCTION Since the early days of semiconductor devices, the

development of microelectronic technology relies largely on the elucidation of electronic states at interfaces between two different materials. For example, electronic interactions at such interfaces form the basis for the operation of a transistor [1]. Moreover, the understanding of quantum effects i.e. electronic energy quantization in the Si two-dimensional electron inversion layer enables a correct description of device characteristics such as tunneling current and oxide physical thickness [2]. In contrast to conventional semiconductors, transition metal oxides sustain complicated couplings of many active degrees of freedom – charge, spin, orbital and lattice. Therefore, the interfaces between these oxides could produce new quantum states and raise the opportunity to uncover exotic phenomena which are unexpected in the respective bulk constituents. Recent studies have shown that combining of insulating, nonmagnetic pervoskite oxides, like SrTiO3 and LaMO3 (M=Al or Ti) induces a quasi-two-dimensional electron gas (Q2-DEG) at the interface which shows high conductivity [3,4], magnetism [5], superconductivity [6,7]. Our earlier study proposed a low dimensional (2D) chemical doping, i.e., La doping into SrTiO3 oxide followed by the formation of a superlattice consisting of La-doped and undoped SrTiO3 layers [8], and reported that the electron transport behavior was greatly different from its bulk behavior [9]. A similar low dimensional oxide superlattice (Nb doping instead of La doping) was shown to exhibit large thermoelectric Seebeck coefficient [10] and superconductivity with quantum oscillations of superimposed frequencies in the normal state [11]. These remarkable properties invoke a detailed

investigation of electronic structure to shed light on electronic behavior in theses confined electron systems.

In this Letter, we report first-principles calculations based on density functional theory within local density approximation + Hubbard U (LDA+U) on (SrTiO3)n/(Sr1-xLaxTiO3)1 superlattice (n×1 STO/SLTO SL) (x=0.25). We show that electronic structure of the SL is substantially modified by increasing STO spacer thickness. Additionally, more than one type of conducting electrons occupied multiple sub-bands is revealed. These electrons have distinctly different effective masses and hence transport behaviors. The electronic reconstruction is demonstrated to be a possible explanation of recent experimental results for embedded Q2-DEG in STO.

Figure 1. Supercell of 2×2×(n+1) of the (STO)n/(SLTO)1 SL with a single

monolayer of Sr0.75La0.25TiO3 (SLTO) embedded in a STO spacer of thickness (a) n = 1, (b) n = 3, and (c) n = 5. The dashed brackets in (a) indicate the one-

unit-cell thick SLTO layer.

II. METHODOLOGY The n×1 SL is modeled by a 2×2×(n+1) supercell which is

composed of a single monolayer of Sr0.75La0.25TiO3 and embedded in a STO layer of which the thickness n was varied from 1 to 5 unit cells (Fig. 1). The in-plane lattice parameter is fixed at 2aSTO, where aSTO is the calculated lattice constant of cubic STO (3.895Å), to simulate the mechanical boundary condition imposed by STO substrate. First-principles density

978-1-4244-8191-0/10/$26.00 ©2010 IEEE

functional calculations were performed within the projector augmented wave (PAW) method [12] as implemented in the Vienna Ab initio Simulation Package (VASP) [13,14] with 4×4×2 k-point grid and an energy cutoff 500eV. Bulk SLTO was also modeled by a 3×3×3 supercell with one single La substituting for a Sr atom, corresponding to doping concentration of 3.7%. To treat exchange and correlation effects, we use the LDA+U method with Ud = 5 eV and Jd = 0.64 eV for the Ti d states and Uf = 11 eV and Jf = 0.68 eV for La f states. The large value of Uf for La was used to shift the La f band further up in energy and prevent a spurious mixing with the Ti d bands [15,16]. A full structural optimization was performed within the tetragonal symmetry, i.e. the atomic displacements are allowed exclusively along the c-axis.

III. CALCULATION RESULTS AND DISCUSSION Fig. 2 shows the near-Fermi energy bands of bulk SLTO.

By substituting La for Sr, there is an extra electron occupying Ti t2g orbitals in a charge state between Ti4+ and Ti3+. At the bottom of the conduction band, the Ti-t2g (dxy, dxz, dyx) orbitals are threefold degenerate and the electronic energy shows parabolic dispersion around the Г point.

Figure 2. The band structure of a 3×3×3 SLTO supercell at the bottom of

the conduction band. The dashed line indicated the Fermi level.

In STO/SLTO, the substitution of La for Sr induces differences in atomic bonds, leading to a misfit strain between the SLTO and STO layers. In such a strained state, the symmetry of the TiO6 octahedra may be reduced from Oh to D4h (centrosymmetric tetragonal). Moreover, the stripped-off La-d1 electrons leave a positively charged La-sheet, that need to be screened. The screening could either be electronic or ionic. In the former case, the two-dimensional distribution of the positive La ions produces potential well, in which the electrons become confined. The latter case is performed through an ionic relaxation process, by which the Ti and Sr cations move outward the La-sheet while O anions toward. Such a polar distortion leads to a further reduction in the

symmetry of the TiO6 octahedra to C4v. As a result, the threefold degeneracy of the t2g manifold is removed. Fig. 3 shows the near-Fermi energy bands of 1×1 (a) and 5×1(b) SL. For a 1×1 SL the dxy orbital splits off about 10meV, as can be noticed from the bands in Fig. 3(a). With increasing the STO thickness to 5 unit-cells, the dxy orbital splits up to 40meV and becomes predominantly occupied [Fig. 3(b)]. We found that this splitting is consistent with that in the SrTiO3/LaAlO3 (STO/LAO) heterostructure. Particularly, x-ray absorption spectroscopy results showed that the dxy orbital has a smaller energy than the (dyz, dxz) ones by 50meV and becomes the first

Figure 3. The band structure of (a) 1×1 and (b) 5×1 STO/SLTO superlattice at the bottom of the conduction band. The dashed

lines indicate the Fermi level in each case.

available states for conducting electrons when the LAO thickness exceeds a critical value of 4 unit-cells [17]. This multiple sub-band occupancy of the conducting electrons would responsible for the quantum oscillation of superimposed frequencies that has recently reported for a similar system of Nb-doped STO embedded in STO [11].

To understand the transport properties of the conducting carriers, the dispersion of the multiple sub-bands is considered in detail. As can be seen from Fig. 3, at the 1×1 stacking period the dyz and dzy bands still show a parabolic dispersion near the Г point while the dxy band is already bent down along the out-of-plane Г-Z direction. With increasing the STO thickness to 5 unit-cells, the lowest dxy band becomes very flat along the Г-Z direction and the width of its PDOS peak is further reduced. In all the case, the band dispersions along the in-plane Г-Χ direction are almost unchanged. The strongly reduced dispersion and the associated enhancement of carrier confinement with STO thickness would lead to an enhanced Seebeck coefficient S. For a degenerate semiconductor, the S can be expressed in terms of DOS effective mass md by [18]:

( (1)

where ne is the carrier concentration. We have performed the calculation of the electron band-effective-masses near the Г point within the parabolic band approximation. From the band effective masses the DOS effective masses were estimated. The results are shown in the Table I.

TABLE I. CALCULATED DENSITY OF STATES (DOS) EFFECTIVE MASS OF ELECTRONS IN STO/SLTO SUPERLATTICE OF DIFFERENT STACKING SEQUENCES. ALL VALUES ARE IN UNITS OF A FREE ELECTRON MASS.

Stacking sequence

(dxz,dyz) dxy

md md

1×1

2×1

3×1

4×1

5×1

0.4

0.4

0.4

0.4

0.4

4.1

4.3

5.2

5.9

6.7

The DOS effective masse of the (dyz, dxz) electrons is hardly changed with stacking period. However, the DOS effective mass of dxy electrons is strongly increased. This behavior is consistent with the band dispersion behavior (Fig. 3). For a 5×1 SL, where the dxy orbital is preferentially occupied the DOS effective mass of 6.7m0 was obtained for the dxy electrons. To compare this calculated value with experimental result, the DOS effective mass for a SL composed of alternate layers of

one-unit-cell thick SrTi0.8Nb0.2O3 and 9-unit-cell thick STO spacer was estimated by using Eq. (1) and experimental parameter from [10]. The estimation results in md =9.3m0, leading to an enhanced thermoelectric Seebeck coefficient. On the other hand, SL structures have long been known for effectiveness in reducing thermal conductivity due to interface reflection of phonon at the interface. The strong lattice distortions near the interface would further reduce thermal conductivity by phonon scattering, and hence enhance thermoelectric figure of merit. Therefore, both the electronic reconstruction and the structural distortion found in the STO/SLTO SL would contribute to an enhanced thermoelectricity.

IV. CONCLUSION In summary, we have presented detailed electronic and

transport properties of the (STO)n/(SLTO)1 SL from first-principle density functional calculation. It is found that the electronic structure of the Ti t2g states is dramatically different from bulk SLTO and substantially changed with the STO spacer thickness. This electronic reconstruction results in multi-type of conducting carriers which can be distinguished by effective mass and hence transport behavior. Our results are consistent with experiments and demonstrated to provide possible origins of recent experimental findings. We hope our will inspire further experiments to clarify the roles and the effects of the multiple types of electrons and compare systematically the embedded Q2-DEG in question and that at the STO/LAO interface.

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