Re-entrant relaxor ferroelectricity of methylammonium lead iodide

Haiyan Guo,Peixue Liu,Shichao Zheng,Shixian Zeng,Na Liu,Seungbum Hong 한국물리학회 2016 Current Applied Physics Vol.16 No.12

We have performed a piezoresponse force microscopy (PFM) study on methylammonium lead iodide (MAPbI3) thin films in normal (non-resonance, non-band-excitation) contact mode. In contrast to the ferroelectric Pb0.76Ca0.24TiO3 (PCT) control sample, a typical ferroelectric response was not observed. However, a nonlinear electric field dependence of the local PFM amplitude was found in MAPbI3, similar to PCT. An analysis combining results on structure, dielectric dispersion, and weak ferroelectricity demonstrates that MAPbI3 is actually a re-entrant relaxor ferroelectric which, upon cooling, enters into a relaxor phase below its ferroelectric phase transition at ~327 K, due to the balance between the long range ferroelectric order and structural methylammonium group orientational disorder. The ferroelectricity at room temperature is compromised due to the re-entrant relaxor behavior, causing the poor polarization retention or weak ferroelectricity. Our findings essentially conciliate the conflicting experimental results on MAPbI3's ferroelectricity and are beneficial both for basic understanding as well as for device applications.

A Brief Review on Relaxor Ferroelectrics and Selected Issues in Lead-Free Relaxors

Chang Won Ahn,Chang-Hyo Hong,Byung-Yul Choi,Hwang-Pill Kim,Hyoung-Su Han,황영훈,Wook Jo,Ke Wang,Jing-Feng Li,Jae-Shin Lee,Ill Won Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12

Relaxor ferroelectricity is one of the most widely investigated but the least understood material classes in the condensed matter physics. This is largely due to the lack of experimental tools that decisively confirm the existing theoretical models. In spite of the diversity in the models, they share the core idea that the observed features in relaxors are closely related to localized chemical heterogeneity. Given this, this review attempts to overview the existing models of importance chronologically, from the diffuse phase transition model to the random-field model and to show how the core idea has been reflected in them to better shape our insight into the nature of relaxor-related phenomena. Then, the discussion will be directed to how the models of a common consensus, developed with the so-called canonical relaxors such as Pb(Mg1/3Nb2/3)O3 (PMN) and (Pb, La)(Zr, Ti)O3 (PLZT), are compatible with phenomenological explanations for the recently identified relaxors such as (Bi1/2Na1/2)TiO3 (BNT)-based lead-free ferroelectrics. This review will be finalized with a discussion on the theoretical aspects of recently introduced 0−3 and 2−2 ferroelectric/relaxor composites as a practical tool for strain engineering.

Observation of ferroelectricity induced by defect dipoles in the strain-free epitaxial CaTiO₃ thin film

Yang, S.M.,Moon, S.J.,Kim, T.H.,Kim, Y.S. Elsevier 2014 Current Applied Physics Vol.14 No.5

CaTiO<SUB>3</SUB> is a well-known incipient ferroelectric material that does not undergo a ferroelectric phase transition in spite of the intriguing dielectric constant behavior. Especially, unlike a prototypical incipient ferroelectric SrTiO<SUB>3</SUB>, the paraelectric state of CaTiO<SUB>3</SUB> cannot be easily destroyed by small perturbations, including cation doping and epitaxial strain. We present that a nearly strain-free epitaxial CaTiO<SUB>3</SUB> film grown at a low oxygen partial pressure exhibits polarization-voltage hysteresis loops and the distinct difference of piezoresponse force microscopy phase signals, implying that a ferroelectric phase is induced. Such results are shown even at room temperature. We suggest that the observed ferroelectric behavior in CaTiO<SUB>3</SUB> film comes from the defect dipoles composed of vacancies inside the film. Using electron-probe microanalysis and optical absorption spectra measurements, we found that CaTiO<SUB>3</SUB> film has considerable Ca and O vacancies, forming the localized defect state in electronic structure. This work highlights the importance of vacancies and their clusters, such as defect dipoles, in understanding the electronic properties of perovskite oxide thin films, including ferroelectricity.

Observation of ferroelectricity induced by defect dipoles in the strainfree epitaxial CaTiO3 thin film

양상모,문순재,김태헌,김용수 한국물리학회 2014 Current Applied Physics Vol.14 No.5

CaTiO3 is a well-known incipient ferroelectric material that does not undergo a ferroelectric phase transition in spite of the intriguing dielectric constant behavior. Especially, unlike a prototypical incipient ferroelectric SrTiO3, the paraelectric state of CaTiO3 cannot be easily destroyed by small perturbations, including cation doping and epitaxial strain. We present that a nearly strain-free epitaxial CaTiO3 film grown at a low oxygen partial pressure exhibits polarizationevoltage hysteresis loops and the distinct difference of piezoresponse force microscopy phase signals, implying that a ferroelectric phase is induced. Such results are shown even at room temperature. We suggest that the observed ferroelectric behavior in CaTiO3 film comes from the defect dipoles composed of vacancies inside the film. Using electron-probe microanalysis and optical absorption spectra measurements, we found that CaTiO3 film has considerable Ca and O vacancies, forming the localized defect state in electronic structure. This work highlights the importance of vacancies and their clusters, such as defect dipoles, in understanding the electronic properties of perovskite oxide thin films, including ferroelectricity.

Dielectric and Ferroelectric Properties of Nb Doped BNT-Based Relaxor Ferroelectrics

Maqbool, Adnan,Hussain, Ali,Malik, Rizwan Ahmed,Zaman, Arif,Song, Tae Kwon,Kim, Won-Jeong,Kim, Myong-Ho Materials Research Society of Korea 2015 한국재료학회지 Vol.25 No.7

The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}Ti_{(1-x)}Nb_xO_3-0.01SrZrO_3$ (BNBTNb-SZ, with ${\chi}=0$, 0.01 and 0.02) ceramics have been investigated. X-ray diffraction patterns revealed that all ceramics have a pure perovskite structure with tetragonal symmetry. The grain size of the ceramics slightly decreased and a change in grain morphology from square to spherical shape was observed in the Nb-doped samples. The maximum dielectric constant temperature ($T_m$) increases with increasing amount of Nb; however, ferroelectric-relaxor transition temperature ($T_{F-R}$) and maximum dielectric constant (${\varepsilon}_m$) values decrease gradually. Nb addition disrupted the polarization hysteresis loops of the BNBT-SZ ceramics by leading a reduction in the remnant polarization coercive field and piezoelectric constant.

Quest for Hydrogen Environments in Hydrogen-Bonded Systems

김세헌 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.6

We performed proton high-resolution nuclear magnetic resonance (NMR) measurements on KH2PO4 ferroelectrics. The 1H high-resolution NMR measurements were performed using the magic-angle spinning technique, which removes the proton-proton dipolar coupling and the chemical shift anisotropy in solid-state materials. High-resolution magic-angle spinning 1H NMR spectroscopy provides information on the chemical structure in the KH2PO4 system. From the measured chemical shift data, we determined the oxygen separation distance of the O-H· · ·O hydrogen bond. The localized hydrogen position of the environments near heavy atoms can be depicted using Morse potentials, which provide the wave function of the eigenstate and the probability distribution of hydrogen in the local structure based on the solutions of the Schr¨odinger equation.

Ferroelectric domain patterns and domain boundary imprint in the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-9%PbTiO3 as observed by using piezoresponse force microscopy

S.-H. Lee,T.-Y. Koo,Y. H. Jeong 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12

Piezoresponse force microscopy is used to observe the ferroelectric domain structures of a typical relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-9%PbTiO3. Detailed structural phases are identified by analyzing the domain patterns from the viewpoint of symmetry. Sequential phase transitions, starting from a rhombohedral phase at room temperature to a tetragonal phase via an intermediate monoclinic one and then to a cubic phase, are observed as the temperature is raised to 500 K. The system also undergoes the same phase sequence, from rhombohedral to monoclinic to tetragonal, as a function of the applied electric field. The domain boundaries are found to be spatially fixed and unchanged despite the multiple phase transition sequence that the system undergoes as the temperature is raised. Contrastingly, this imprint effect is missing in the field-driven phase transition sequence. The imprint effect is presumably caused by electric charges on the domain boundaries, possibly arising from local charge imbalances in the relaxor ferroelectric.

Nd가 치환된 Bi4-xNdxTi3O12 세라믹스의 구조 및 전기적 특성 변화

최기쁨,조삼연,전도현,부상돈,이경자,이민구 한국물리학회 2015 새물리 Vol.65 No.7

Bismuth-layer-structured ferroelectric/piezoelectric Bi4−xNdxTi3O12 (BNdT) ceramics in which the Nd substitution was controlled from x = 0.25 to 1.00 were prepared by using the conventional solid-state-reaction method. Structural analysis by using X-ray diffraction (XRD) showed that all the BNdT ceramics had a polycrystalline structure without second phases, which was consistent with the data for Bi4Ti3O12 (JCPDS No. 35-0795). We found that the BNdT ceramics had grains with elongated shapes. The change in the orientation ratio of a − b plane in the grains with increasing Nd substitution was found to be similar to the changes in their electrical properties. In particular, a notable improvement in the electrical properties was observed in the x = 0.75 - 0.90 composition ratio of the BNdT ceramics. For the Bi3.1Nd0.9Ti3O12 (x = 0.90) ceramics, the values of the dielectric constant and the piezoelectric coefficients exhibited maximum values of about 209 and 15 pC/N, respectively. On the other hand, with increasing Nd concentration, the phase transition temperature (Tc) continuously decreased from 613 ℃ (Bi3.75Nd0.25Ti3O12, x = 0.25) to 218 ℃ (Bi3.00Nd1.00Ti3O12, x = 1.00). These results suggest that controlling the Nd substitution in BNdT ceramics is essential for changing the dielectric constant and piezoelectric coefficients of bismuth-layer-structured piezoelectric materials. Nd 치환량을 조절하여 Bi4-xNdxTi3O12 (BNdT) 세라믹스의 조성을 x = 0.25에서 1.00까지 범위에서 제어한 세라믹스를 고상반응법으로 제작하였다. X-선 회절 분석을 통해 모든 시료에서 다결정의 Bi4Ti3O12 구조가 잘 형성되었음을 확인 하였다. Nd 치환량에 따른 구조 변화를 살펴보기 위해 조사된 a-b 방향면들의 비율 변화는 전기적 특성 변화와 밀접한 관계가 있는 것으로 확인 되었다. BNdT 세라믹스는 Nd 치환량이 증가함에 따라서 x = 0.75 이상의 조성비에서 주목할만한 전기적 특성 향상을 보였으며, x = 0.90의 조성비에서 가장 우수한 특성을 나타내었다. Bi3.1Nd0.9Ti3O12 세라믹스 (x = 0.90)에서 측정된 유전상수 값과 압전계수 값은 각 각 209와 15 pC/N으로 최대값을 나타내었으며, 항전기장 (2Ec) 값은 38 kV/cm 로 최소값을 보였다. 이러한 결과들을 통해서 BNdT 세라믹스에서 Nd 치환에 따른 최적의 조성비를 확인하였다.

Synthesis and ferroelectric behavior of Gd doped BNT ceramics

Vijayeta Pal,R.K. Dwivedi,O.P. Thakur 한국물리학회 2014 Current Applied Physics Vol.14 No.1

In the present work, polycrystalline (Bi1xGdx)0.5Na0.5TiO3 (BGNT) ceramics with low amount of rare earth ion Gd3þ (x ¼ 0, 0.02, 0.03, 0.04) have been synthesized by a semiewet technique. XRD patterns show single phase formation for all the samples with a rhombohedral structure at room temperature. FESEM images show decrease in grain size with Gd concentration. The temperature dependence of dielectric constant has revealed that the depolarization temperature ‘Td’ decreases with increasing x and the temperature ‘Tm’ of maximum dielectric constant increases initially for x ¼ 0.02 thereafter decreases. All the samples have shown saturated hysteresis (PeE) loop at room temperature. The BGNT ceramic system for composition, x ¼ 0.02 exhibits improved piezoelectric properties and strong ferroelectricity. With increasing temperature, polarization has been found to be reduced and deformed PeE loops are observed around ‘Td’.

Effect of Nb Doping on the Dielectric and Strain Properties of Lead-free 0.94(Bi_1/2Na_1/2)TiO₃-0.06BaTiO₃ Ceramics

Han, Hyoung-Su,Hong, In-Ki,Kong, Young-Min,Lee, Jae-Shin,Jo, Wook The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.2

$(Bi_{1/2}Na_{1/2})_{0.94}Ba_{0.06}(Ti_{1-x}Nb_x)O_3$ (BNBTxNb) ceramics were investigated in terms of the crystal structure as well as the ferroelectric, dielectric, and piezoelectric properties. While little change was observed in the microstructure except for a slight decrease in the average grain size, a significant change was noticed in the temperature dependence of dielectric and piezoelectric properties. It was shown that the property changes are closely related to the downward shift in the position of the ferroelectric-to-relaxor transition temperature with increasing amount of Nb doping. A special emphasis is put on the fact that Nb doping is so effective at decreasing the ferroelectric-to-relaxor transition temperature that even at no more than 2 at.% Nb addition, the transition temperature was already brought down slightly below room temperature, resulting in the birth of a large strain at 0.46 %, equivalent to $S_{max}/E_{max}=767pm/V$.