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S Torgova, S P Sreenilayam, Yu P Panarin, O Francescangeli, F Vita, J K Vij, E Pozhidaev, M Minchenko, C Ferrero, A Strigazzi
Bent-core liquid crystals based on 1,2,4-oxadiazole as a central unit have been the first mesogens to exhibit a ferroelectric response in the nematic phase. This behavior has been widely recognized as due to the presence of smectic-like polar cybotactic clusters permeating the nematic phase. Unfortunately, these compounds exhibited rather high melting points, about 120 °C, due to the presence of four benzene rings in the molecules. Here we describe the synthesis and physical characterization of a new series of BC mesogens, featuring the same bent core as the previous compounds but shorter outer substituents...
August 16, 2017: Physical Chemistry Chemical Physics: PCCP
Sharada Govinda, Bhushan P Kore, Menno Bokdam, Pratibha Mahale, Abhinav Kumar, Somnath Pal, Biswajit Bhattacharyya, Jonathan Lahnsteiner, Georg Kresse, Cesare Franchini, Anshu Pandey, D D Sarma
Dielectric constants of MAPbX3 (X = Br, I) in 1 kHz-1 MHz range show strong temperature dependencies near the room temperature in contrast to the nearly temperature independent dielectric constant of CsPbBr3. This strong temperature dependence for MAPbX3 in the tetragonal phase is attributed to the MA(+) dipoles rotating freely within the probing time scale. This interpretation is supported by ab initio molecular dynamics simulations on MAPbI3 that establish these dipoles as randomly oriented with a rotational relaxation time scale of ~7 ps at 300 K...
August 16, 2017: Journal of Physical Chemistry Letters
Guohua Dong, Ziyao Zhou, Xu Xue, Yijun Zhang, Bin Peng, Mengmeng Guan, Shishun Zhao, Zhongqiang Hu, Wei Ren, Zuo-Guang Ye, Ming Liu
Yttrium iron garnet (YIG) is of great importance in RF/microwave devices for its low loss, low intrinsic damping and high permeability. Nevertheless, tuning of YIG based multiferroics is still a challenge due to its near zero magnetostriction and the difficulty of building epitaxial interface between ferromagnetic garnet and ferroelectric perovskite phases. In this work, the vertical aligned heterostructure of YIG:BTO/STO(001) with local epitaxial interface between BTO and YIG is well-constructed, where the single crystal BTO pillars are embedded in YIG matrix...
August 15, 2017: ACS Applied Materials & Interfaces
Jinyan Zhao, Wei Ren, Gang Niu, Nan Zhang, Guohua Dong, Lingyan Wang, Ming Liu, Peng Shi, Zuo-Guang Ye
Bismuth sodium titanate, Bi0.5Na0.5TiO3 (BNT), is a promising lead-free ferroelectric material. However, its potential applications have not been fully explored, mainly because of the complex domain structure arising from its intricate phase transitions. A deep and thorough study of its domain structure and polarization switching behavior will greatly help with understanding the polarization nature and with promoting future applications. In this work, we demonstrate that BNT polycrystalline films possess a highly ordered out-of-plane polarization (self-polarization) and randomly oriented in-plane polarizations...
August 15, 2017: ACS Applied Materials & Interfaces
Andrés Gómez, José Manuel Vila-Fungueiriño, Rahma Moalla, Guillaume Saint-Girons, Jaume Gázquez, María Varela, Romain Bachelet, Martí Gich, Francisco Rivadulla, Adrián Carretero-Genevrier
Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO3 thin film on Si(001) is explored...
August 15, 2017: Small
Yao Sun, Zhigang Hu, Dan Zhao, Kaiyang Zeng
Experimental investigation of functional properties of metal-organic frameworks (MOFs) at nanoscale precision is challenging and rarely reported. In this study, we report the piezo- and ferroelectric properties of NUS-6 MOF nanocrystals using dual AC resonance tracking piezoresponse force microscopy and piezoresponse force spectroscopy for the first time. Both NUS-6-(Hf) and NUS-6-(Zr) nanocrystals displayed anomalous piezoelectricity with the calculated piezoelectric coefficient dzz constants of 2.0-3.5 pm V(-1) and 1...
August 14, 2017: Nanoscale
Yi Yu, Dandan Zhang, Peidong Yang
A Ruddlesden-Popper (RP) type structure is well-known in oxide perovskites and is related to many interesting properties such as superconductivity and ferroelectricity. However, the RP phase has not yet been discovered in inorganic halide perovskites. Here, we report the direct observation of unusual structure in two-dimensional CsPbBr3 nanosheets which could be interpreted as the RP phase based on model simulations. Structural details of the plausible RP domains and domain boundaries between the RP and conventional perovskite phases have been revealed on the atomic level using aberration-corrected scanning transmission electron microscopy...
August 10, 2017: Nano Letters
Kenji Kiyohara, Yasushi Soneda, Kinji Asaka
The phase behavior of ions in porous electrodes is qualitatively different from that in the bulk because of the confinement effect and the interaction between the electrode surface and the electrolyte ions. We found that porous electrodes of which the pore size is close to the size of the electrolyte ions can show ferroelectric phase behaviors in some conditions by Monte Carlo simulations of simple models. The phase behavior of the porous electrodes dramatically changes as a function of the pore size of the porous electrode and that is compared to the phase behavior of typical ferroelectric materials, for which the phase behavior changes as a function of temperature or the composition...
August 10, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Shi-Yu Liu, Yang Meng, Shiyang Liu, De-Jun Li, Yaping Li, Yingdi Liu, Yaogen Shen, Sanwu Wang
With extensive first-principles density-functional calculations, we construct a three-dimensional compositional phase diagram of Ba1-xCaxZryTi1-yO3 (BCZT) with the Ca and Zr content in the ranges of 0 ≤ xCa ≤ 0.2 and 0 ≤ yZr ≤ 1. Our calculations show that, when the Zr content increases, the difference in energy and difference in the structural parameters of the cubic, tetragonal, orthorhombic, and rhombohedral phases of BCZT are reduced. Eventually, all four phases merge into a multiphase with coexisting cubic structures (MPCCS) under Zr-rich conditions, indicating that BCZT undergoes phase transition from a normal ferroelectric (NFE) to a relaxor ferroelectric (RFE), consistent with experimental observations...
August 10, 2017: Physical Chemistry Chemical Physics: PCCP
Haizhong Guo, Qingqing Li, Zhengzhong Yang, Kui-Juan Jin, Chen Ge, Lin Gu, Xu He, Xiaolong Li, Ruiqiang Zhao, Qian Wan, Jiesu Wang, Meng He, Can Wang, Huibin Lu, Yuping Yang, Guozhen Yang
Artificial superlattices constructed with ferromagnetic La0.7Sr0.3MnO3 layer and ferroelectric Ba0.7Sr0.3TiO3 layer were designed and fabricated on SrTiO3 substrates. An epitaxial growth with sharp interfaces between La0.7Sr0.3MnO3 and Ba0.7Sr0.3TiO3 layers was confirmed by scanning transmission electron microscopy and x-ray diffraction. An unambiguous charge transfer involving an electron transferring from the La0.7Sr0.3MnO3 layers to Ba0.7Sr0.3TiO3 layers (Mn(3+)→Mn(4+); Ti(4+)→Ti(3+)) across the interface were resolved by electron energy loss spectra analysis...
August 9, 2017: Scientific Reports
L Sánchez-García, M O Ramírez, C Tserkezis, R Sole, J J Carvajal, M Aguiló, F Díaz, L E Bausá
Increasing Yb(3+) absorption efficiency is currently desired in a number of applications including bio-imaging, photovoltaics, near infrared driven photocatalysis or ultra-short pulsed solid-state lasers. In this work, silver nanoparticles, which are connected forming disordered networks, have been self-assembled on Yb(3+) doped RbTiOPO4 crystals to produce a remarkable enhancement of Yb(3+) absorption, and hence in the photoluminescence of this ion. The results are interpreted taking into account the near-field response of the plasmonic networks, which display strong amplification of the electric field at the maximum of Yb(3+) excitation at around 900 nm, together with the anisotropic character of the Yb(3+) transitions in RbTiOPO4...
August 9, 2017: Nanoscale
A R Damodaran, J D Clarkson, Z Hong, H Liu, A K Yadav, C T Nelson, S-L Hsu, M R McCarter, K-D Park, V Kravtsov, A Farhan, Y Dong, Z Cai, H Zhou, P Aguado-Puente, P García-Fernández, J Íñiguez, J Junquera, A Scholl, M B Raschke, L-Q Chen, D D Fong, R Ramesh, L W Martin
Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO3/SrTiO3 superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a1/a2 phase...
August 7, 2017: Nature Materials
Ronghuan Zhang, Alexandra S Gibbs, Weiguo Zhang, P Shiv Halasyamani, Michael A Hayward
Calcium-for-strontium cation substitution of the a(-)b(0)c(0)/b(0)a(-)c(0)-distorted, cation-ordered, n = 2 Ruddlesden-Popper phase, YSr2Mn2O7, leads to separation into two phases, which both retain an a(-)b(0)c(0)/b(0)a(-)c(0)-distorted framework and have the same stoichiometry but exhibit different degrees of Y/Sr/Ca cation order. Increasing the calcium concentration to form YSr0.5Ca1.5Mn2O7 leads to a change in the cooperative tilting on the MnO6 units to a novel a(-)b(-)c(-)/b(-)a(-)c(-) arrangement described in space group P21/n11...
August 4, 2017: Inorganic Chemistry
Mircea L Dragoman, Mircea Modreanu, Ian M Povey, Sergiu Iordanescu, Martino Aldrigo, Cosmin Romanitan, Dan Vasilache, Adrian Dinescu, Daniela Dragoman
In this letter, we report for the first time very large phase shifts of microwaves in the 1-10 GHz range, in a 1-mm-long gold coplanar interdigitated structure deposited over 6 nm HfxZr1-xO2 ferroelectric grown directly on a high-resistivity silicon substrate. The phase shift is larger than 60o at 1 GHz and 13o at 10 GHz at maximum applied DC voltages of ± 3 V, which can be supplied by a simple commercial battery. In this way, we demonstrate experimentally that the new ferroelectrics based on HfO2 could play an important role in the future development of wireless communication systems for very low power applications...
August 4, 2017: Nanotechnology
Olivier Copie, Nicolas Chevalier, Gwenael Le Rhun, Cindy L Rountree, Dominique Martinotti, Sara Gonzalez, Claire Mathieu, Olivier Renault, Nicholas T Barrett
We present a study of adsorbate screening of surface charge in microscopic ferroelectric domains in a sol-gel grown PbZr0.2Ti0.8O3 thin film. Low energy electron and photoemission electron microscopies were employed to characterize the temperature dependence of surface charge and polarization of ferroelectric domains written by atomic force microscopy. We study the role of charged adsorbates in screening of polarization bound charges. We demonstrate that full-field electron microscopy is suitable for the determination of ferroelectric system properties such as the Curie temperature...
August 4, 2017: ACS Applied Materials & Interfaces
Ming Yang, Amit Kc, A C Garcia-Castro, Pavel Borisov, E Bousquet, David Lederman, Aldo H Romero, Cheng Cen
The NaMnF3 fluoride-perovskite has been found, theoretically, to be ferroelectric under epitaxial strain becoming a promising alternative to conventional oxides for multiferroic applications. Nevertheless, this fluoroperovskite has not been experimentally verified to be ferroelectric so far. Here we report signatures of room temperature ferroelectricity observed in perovskite NaMnF3 thin films grown on SrTiO3. Using piezoresponse force microscopy, we studied the evolution of ferroelectric polarization in response to external and built-in electric fields...
August 3, 2017: Scientific Reports
Giacomo Prando
No abstract text is available yet for this article.
August 4, 2017: Nature Nanotechnology
Jesús-Alejandro Peña-Jiménez, Federico González, Rigoberto López-Juárez, José-Manuel Hernández-Alcántara, Enrique Camarillo, Héctor Murrieta-Sánchez, Lorena Pardo, María-Elena Villafuerte-Castrejón
The solid-state method was used to synthesize single phase potassium-sodium niobate (KNN) co-doped with the La(3+)-Mn(4+) and Eu(3+)-Fe(3+) ion pairs. Structural determination of all studied solid solutions was accomplished by XRD and Rietveld refinement method. Electron paramagnetic resonance (EPR) studies were performed to determine the oxidation state of paramagnetic centers. Optical spectroscopy measurements, excitation, emission and decay lifetime were carried out for each solid solution. The present study reveals that doping KNN with La(3+)-Mn(4+) and Eu(3+)-Fe(3+) at concentrations of 0...
September 28, 2016: Materials
Dinesh Lolla, Manideep Lolla, Ahmed Abutaleb, Hyeon U Shin, Darrell H Reneker, George G Chase
Electrospun polyvinylidene fluoride (PVDF) fiber mats with average fiber diameters (≈200 nm, ≈2000 nm) were fabricated by controlled electrospinning conditions. These fiber mats were polarized using a custom-made device to enhance the formation of the electret β-phase ferroelectric property of the fibers by simultaneous uniaxial stretching of the fiber mat and heating the mat to the Curie temperature of the PVDF polymer in a strong electric field of 2.5 kV/cm. Scanning electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry and Brunauer-Emmett-Teller (BET) surface area analyses were performed to characterize both the internal and external morphologies of the fiber mat samples to study polarization-associated changes...
August 9, 2016: Materials
Rodrigo Vivar-Ocampo, Lorena Pardo, David Ávila, Emilio Morán, Amador M González, Lauro Bucio, María-Elena Villafuerte-Castrejón
Research and development of lead-free piezoelectric materials are still the hottest topics in the field of piezoelectricity. One of the most promising lead-free family of compounds to replace lead zirconate-titanate for actuators is that of Bi0.50Na0.50TiO₃ (BNT) based solid solutions. The pseudo-binary (1 - x)Bi0.50Na0.50TiO₃-xBa1 - yCayTiO₃ system has been proposed for high temperature capacitors and not yet fully explored as piezoelectric material. In this work, the solid solution with x = 0.06 and y = 0...
July 1, 2017: Materials
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