Use Of Ferroelectric Materials Research Articles

Enhancing BiVO4 photoanode performance by insertion of an epitaxial BiFeO3 ferroelectric layer

BiVO4 (BVO) is a promising material as the photoanode for use in photoelectrochemical applications. However, the high charge recombination and slow charge transfer of the BVO have been obstacles to achieving satisfactory photoelectrochemical performance. To address this, various modifications have been attempted, including the use of ferroelectric materials. Ferroelectric materials can form a permanent polarization within the layer, enhancing the separation and transport of photo-excited electron-hole pairs. In this study, we propose a novel approach by depositing an epitaxial BiFeO3 (BFO) thin film underneath the BVO thin film (BVO/BFO) to harness the ferroelectric property of BFO. The self-polarization of the inserted BFO thin film simultaneously functions as a buffer layer to enhance charge transport and a hole-blocking layer to reduce charge recombination. As a result, the BVO/BFO photoanodes showed more than 3.5 times higher photocurrent density (0.65 mA cm−2) at 1.23 VRHE under the illumination compared to the bare BVO photoanodes (0.18 mA cm−2), which is consistent with the increase of the applied bias photon-to-current conversion efficiencies (ABPE) and the result of electrochemical impedance spectroscopy (EIS) analysis. These results can be attributed to the self-polarization exhibited by the inserted BFO thin film, which promoted the charge separation and transfer efficiency of the BVO photoanodes.

On the Development of New Tuning and Inter-Coupling Techniques Using Ferroelectric Materials in the Detection of Dark Matter Axions

Tuning is an essential requirement for the search of dark matter axions employing haloscopes since its mass is not known yet to the scientific community. At the present day, most haloscope tuning systems are based on mechanical devices which can lead to failures due to the complexity of the environment in which they are used. However, the electronic tuning making use of ferroelectric materials can provide a path that is less vulnerable to mechanical failures and thus complements and expands current tuning systems. In this work, we present and design a novel technique for using the ferroelectric Potassium Tantalate (KTaO3 or KTO) material as a tuning element in haloscopes based on coupled microwave cavities. In this line, the structures used in the Relic Axion Detector Exploratory Setup (RADES) group are based on several cavities that are connected by metallic irises, which act as interresonator coupling elements. In this article, we also show how to use these KTaO3 films as interresonator couplings between cavities, instead of inductive or capacitive metallic windows used in the past. These two techniques represent a crucial upgrade over the current systems employed in the dark matter axions community, achieving a tuning range of 2.23% which represents a major improvement as compared to previous works (< 0.1%) for the same class of tuning systems. The theoretical and simulated results shown in this work demonstrate the interest of the novel techniques proposed for the incorporation of this kind of ferroelectric media in multicavity resonant haloscopes in the search for dark matter axions.

Autonomous Design of Photoferroic Ruddlesden-Popper Perovskites for Water Splitting Devices

The use of ferroelectric materials for light-harvesting applications is a possible solution for increasing the efficiency of solar cells and photoelectrocatalytic devices. In this work, we establish a fully autonomous computational workflow to identify light-harvesting materials for water splitting devices based on properties such as stability, size of the band gap, position of the band edges, and ferroelectricity. We have applied this workflow to investigate the Ruddlesden-Popper perovskite class and have identified four new compositions, which show a theoretical efficiency above 5%.

Effects of Interface Trap on Transient Negative Capacitance Effect: Phase Field Model

Ferroelectric materials have received significant attention as next-generation materials for gates in transistors because of their negative differential capacitance. Emerging transistors, such as the negative capacitance field effect transistor (NCFET) and ferroelectric field-effect transistor (FeFET), are based on the use of ferroelectric materials. In this work, using a multidomain 3D phase field model (based on the time-dependent Ginzburg–Landau equation), we investigate the impact of the interface-trapped charge (Qit) on the transient negative capacitance in a ferroelectric capacitor (i.e., metal/Zr-HfO2/heavily doped Si) in series with a resistor. The simulation results show that the interface trap reinforces the effect of transient negative capacitance.

(Ba/Pb)xSr1−xTiO3 based capacitive sensor with LaNiO3 electrode for higher tunability

The high tunability range of capacitive sensors can be achieved by the use of ferroelectric materials due to its perovskite structure. Thin films provide better utilization of properties comparative to bulk but greatly affect by the surface on which it deposited. In this work thin films of BaxSr1−xTiO3 (BST) and PbxSr1−xTiO3 (PST) are developed with x = 0.3 & 0.7. Thin films without doping of Sr are also developed for comparison. The capacitors Al/Si/BST/Al and Al/Si/PST/Al are fabricated in parallel plate structure using the sol–gel processing technique with Al as metal electrodes and BST/PST as the dielectric material. A new parallel plate capacitor with the introduction of Lanthanum Nickel Oxide (LNO) thin film with the preferred (100) orientation between Si substrate and BST/PST is proposed in this work. Crystallinity and orientation of BST/PST on Si and BST/PST over LNO are observed by X-ray diffraction (XRD). The average grain size and uniformity of thin films are confirmed by scanning electron microscopy (SEM) images. The capacitances are measured at 50 mV and 70 mV using LCR meter. The highest capacitance of 79.6pF is observed for Al/Si/LNO/BST/Al. Impedance spectroscopy reveals the decrement in impedance with doping of Sr and tunability range of LNO based BST/PST capacitor is much higher compared to non-LNO capacitors. Tunability with BST material reaches 57% at frequency 2.98 kHz and the PST attains a value of 33.8% at frequency 1.44 KHz.

Effect of Internal Electric Fields on Charge Carrier Dynamics in a Ferroelectric Material for Solar Energy Conversion.

Spontaneous polarization is shown to enhance the lifetimes of photogenerated species in BaTiO3 . This is attributed to polarization-induced surface band bending acting as a thermal barrier to electron/hole recombination. The study indicates that the efficiencies of solar cells and solar fuels devices can be enhanced by the use of ferroelectric materials.

Photovoltaic properties of Bi2FeCrO6 films epitaxially grown on (100)-oriented silicon substrates.

We demonstrate the promising potential of using perovskite Bi2FeCrO6 (BFCO) for niche applications in photovoltaics (PV) (e.g. self-powered sensors that simultaneously exploit PV conversion and multiferroic properties) or as a complement to mature PV technologies like silicon. BFCO thin films were epitaxially grown on silicon substrates using an MgO buffer layer. Piezoresponse force microscopy measurements revealed that the tensile strained BFCO phase exhibits a polarization predominantly oriented through the in-plane direction. The semiconducting bandgap of the ordered BFCO phase combined with ferroelectric properties, opens the possibility of a ferroelectric PV efficiency above 2% in a thin film device and the use of ferroelectric materials simultaneously as solar absorber layers and carrier separators in PV devices. A large short circuit photocurrent density of 13.8 mA cm(-2) and a photovoltage output of 0.5 V are typically obtained at FF of 38% for BFCO devices fabricated on silicon. We believe that the reduced photovoltage is due to the low diffusion length of photogenerated charge carriers in the BFCO material where the ferroelectric domains are predominately oriented in-plane and thus do not contribute efficiently to the photocharge separation process.

ChemInform Abstract: Defect Chemistry in Ferroelectric Perovskites: Long Standing Issues and Recent Advances

AbstractReview: 42 refs.

Defect chemistry in ferroelectric perovskites: long standing issues and recent advances.

Accurate control of residual defect density is required for reliable investigation and use of ferroelectric materials. After reviewing the long term endeavor to decrease defect contributions in bulk materials, which reached mass production decades ago, recent challenges are underlined. These mostly result from the continuous trend towards integration which has reached the nanometre range. The contribution of solid state chemistry is of key relevance for improving the present processing routes and suggesting alternative ones, for example by controlling a large density of charged defects to reach unprecedented functionalities. Some of these breakthroughs are reviewed.

Application of a sensitive catalytic reactor to the study of CO oxidation over SrTiO3(100) and BaTiO3/SrTiO3(100) ferroelectric surfaces

The use of ferroelectric materials as adsorbents or catalysts could be a promising way to control surface chemical reactions by tuning the ferroelectric polarization. In this context, the oxidation of carbon monoxide over well‐defined SrTiO3(100) and BaTiO3/SrTiO3(100) perovskite surfaces was investigated under stoichiometric gas‐phase conditions at a total pressure of 3 Torr, in the 100–300 °C temperature range. To this aim, an ultrahigh vacuum‐compatible reactor equipped with external laser heating, and specially designed to detect small yields of gaseous products by mass spectrometry, was used. Prior to the catalytic tests, with the help of Auger electron spectroscopy, a sample cleaning procedure under low oxygen pressure was established in order to remove carbon impurities. The as‐prepared surfaces appear poorly active in CO oxidation, but their activity increases if a high‐temperature pre‐annealing treatment under ultrahigh vacuum is applied in order to produce oxygen vacancies, which act as adsorption and/or reaction sites. The activity of the bare SrTiO3 substrates, whether doped with Nb or not, is similar to that of the supported BaTiO3 films, but the latter lose less activity upon evacuation/reaction cycles. Isotopic labeling experiments using 18O2 show that the reaction involves CO (and O2) dissociation, and that lattice oxygen participates to the reaction via the so‐called Mars–van Krevelen mechanism. Copyright © 2014 John Wiley &amp; Sons, Ltd.

I-V Characteristics of a Static Random Access Memory Cell Utilizing Ferroelectric Transistors

Due to the unique properties of hysteresis and nonlinearity, the use of ferroelectric materials in memory devices is widely researched. This paper presents the current-voltage (I-V) characteristics of a FeFET in the Static Random Access Memory (SRAM) cell. Empirical data will be analyzed using a variety of setup configurations using both MOSFETs as well as FeFETS. The drain current was measured with different gate and drain voltages while polarizing the ferroelectric material. Based on the empirical data, comparisons were made between the different MOSFET and FeFET configurations.

Analysis and design of smart electromagnetic structures

Use of ferroelectric materials to improve antenna performance is an area of active research.Applying an electric field across a ferroelectric used as the dielectric in an antenna enablestuning the antenna performance. Ferroelectrics also have coupled electro-mechanicalbehavior due to which they are sensitive to mechanical strains and fluctuations in ambienttemperature. Use of ferroelectrics in antenna structures, especially those subject tomechanical and thermal loads, requires knowledge of the phenomenological relationshipbetween the ferroelectric properties of interest (especially the dielectric permittivity) andthe external physical variables, namely electric field(s), mechanical strains andtemperature. To this end, a phenomenological model of ferroelectric materials based on theDevonshire thermodynamic theory is presented. This model is then used to obtain arelationship expressing the dependence of the dielectric permittivity on the mechanicalstrain, applied electric field and ambient temperature. The relationship is compared againstpublished experimental data and other models in the literature. A model relating theferroelectric loss tangent to the applied electric field and temperature is also discussed.Subsequently, relationships expressing the dependences of the antenna operatingfrequency and radiation efficiency on those external physical quantities are described.

CHARACTERIZING AN ANALOG AMPLIFIER UTILIZING A FERROELECTRIC TRANSISTOR

ABSTRACT The use of ferroelectric materials for digital memory devices is widely researched and implemented, but ferroelectric devices also posses unique characteristics that made them have interesting and useful properties in analog circuits. Because ferroelectric transistors posses the properties of hysteresis and nonlinearity, an analog amplifier containing an FeFET has very different characteristics than one with a traditional FET. This paper characterizes the properties of a simple analog amplifier using both a traditional FET and a ferroelectric FET. The characterization includes voltage transfer, gain, frequency response, and operating modes. Because of the hysteresis effects the FeFET amplifier has two distinct operating modes, each with significantly different properties. These two regions have very different gain characteristics and are nonlinear. This has the effect of being able to program the FeFET to have two different voltage transfer/current characteristics with a single device. This can allow a flexible circuit that can change its analog properties on-the-fly with only a programming pulse. Modeled and measured data are presented showing the characteristics of this device. Comparisons are made between the ferroelectric device and the properties of a standard analog amplifier. Potential benefits and possible uses of such a device are presented.

One-dimensional tunable ferroelectric photonic crystals based on Ba0.7Sr0.3TiO3/MgO multilayer thin films

Tunable photonic crystals (PCs) have attracted much attention in the past decade because of their various applications, such as ultrafast optical filters and optical waveguides with add–drop functionalities. One way of achieving tunability is to make use of ferroelectric materials since the refractive index of ferroelectric materials can be electrically tuned through the electro-optic effect. In this paper, we present our work on developing a tunable one-dimensional (1D) PC based on a Ba0.7Sr0.3TiO3/MgO multilayer structure. The photonic band structures and band gap maps of the PC were calculated by using the plane-wave expansion (PWE) method. It is found that the gap center linearly shifts with the change in the refractive index of Ba0.7Sr0.3TiO3. A ferroelectric 1D PC consisting of a Ba0.7Sr0.3TiO3/MgO multilayer thin film was epitaxially deposited on a MgO (001) single-crystal substrate by pulsed laser deposition. A photonic band gap in the visible region is observed in the transmission spectrum of the multilayer thin film. The center wavelength of the band gap is ∼464 nm, which agrees with the simulation results obtained by the transfer matrix method. The band gap can be tuned by applying an electric field E. The band gap shifts by about 2 nm when the thin film is subjected to a dc voltage of 240 V (E∼12 MV/m). This shift corresponds to an ∼0.5% change in the refractive index of the Ba0.7Sr0.3TiO3 layer, as calculated by the PWE method.

Separation of the Pyro- and Piezoelectric Response of Electroactive Polymers for Sensor Applications

One of the main problems for the use of ferroelectric materials for sensor applications, especially for tactile sensors, is the separation of the pyro- and piezoelectric responseproduced by temperature and pressure changes, respectively. We present two different approaches to achieve this goal. The first approach is based on the study of the signal in the frequency domain and uses a signal processing to separate the approach is based on a double layer configuration of electroactive polymers. In this case, the piezoelectric response is equal in each layer, whereas, the pyroelectric response dominates in the layer exposed to the temperature variations. The pyro- and piezoelectric responses are separated by estimating the diference between the signals of two layers and the signal from one of the layers, correspondingly.

Enhanced Electrode Kinetics in Electrochemical CO2 and SO2 Gas Sensors with Ferroelectric Dispersed Composite

The demand for reliable and economical SO 2 and CO 2 gas sensors with a large detection range, high sensitivity, good selectivity, rapid response and high accuracy has become evident. In addition, these gases are very difficult to detect by conventional gas sensors for the reason of its high stability at ordinary temperatures. Many kinds of compact sensors using various materials, such as solid electrolytes, mixed oxides, zeolites, and so on have been investigated so far. None of them seems to have achieved sufficient performance characteristics for practical use. Among these, solid electrolytes based sensors are of particular interest again from the viewpoint of low-cost, simple structure, high sensitivity and simplicity of above mentioned gas detection mechanism. The electrochemical SO 2 and CO 2 gas sensors are made using ferroelectric materials dispersed sulphate and carbonate electrolytes, respectively. The performance of sensing electrode sensors is improved due to use of ferroelectric materials with proper proportion. Also, both the response time and the recovery time are found decreased considerably, i.e. sensors quickly respond to change in gas concentration. The ferroelectric property of second phase not only enhances the defect concentration at the grain boundary interface, leading to increase in ionic conductivity, but also promotes oxy-ion activity with improved reaction kinetics. These pronounced effects are discussed in the light of presence of ferroelectric phase in the electrolyte as well as electrodes.

Scanning Probe Microscopy for Imaging Magnetic and Ferroelectric Patterns on a Nanoscale

Scanning Probe Microscopy (SPM) has developed in a powerful tool to image different physical properties on the surface of solid samples. Two examples of dedicated Scanning Force Microscopy (SFM or AFM) are presented here: ii) In Piezo-response Force Microscopy (PFM) an oscillating bias potential is applied to a force sensor in order to image ferroelectric domain patterns, and i) in Magnetic Force Microscopy (MFM) an oscillating magnetic probe is used to visualize the stray field on magnetic samples.i) The use of ferroelectric materials in the development of fast and non-volatile random access memory is very promising. PFM can be applied to study domain formation on a nanometer scale, and to conclude about the influence of grain boundaries on ferroelectric domain patterns. Furthermore, it is possible to use PFM for domain switching and writing. Examples are shown on single crystalline bulk material and on patterned thin film samples.ii) The density in magnetic data storage has increased by almost three orders of magnitude in the last decade. MFM is very suitable for imaging these small magnetic patterns, but it is necessary to use high-resolution magnetic probes in a sophisticated operation mode in order to obtain the required 20 nm magnetic resolution. Examples are shown on in-plane and on perpendicular recording media, as well as on patterned research samples.

Fabrication and Properties of Thin Microwave Absorbers of Ferroelectric Materials Used in Mobile Telecommunication Frequency Bands

High-frequency dielectric and microwave absorbing properties have been investigated in ferroelectric materials (BaTiO(BT), (1-x)Pb)O-xPbTiO(PMN-PT), (1-x)PbO-xPb(Zn_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O(PMN-PZN) for the aim of thin microwave absorbers in the frequency range of mobile telecommunication. The specimenns are prepared by conventional ceramic processing and complex permittivity has been measured by transmission/reflection method. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave range and their domiant loss mechanism is considered to be domain wall relaxation. The microwave absorbance of BT 0.9PMN-0.1PT, and 0.8PMN-0.2PZN specimen (determined at 2) are found to be 99.5% (at a thickness of 4.5 mm), 50% (2.5 mm), and 30% (2.5 mm), respectively. It is suggested that PMN-PT or PMN-PZN ferroelectrics are good candidate materials for the spacer of λ/4 absorber. The use of ferroelectric materials is effective in reducing the thickness of absorber with their advantage of high dielectric constant.

Design of a low-cost 2-D beam-steering antenna using ferroelectric material and CTS technology

The design of a new low-cost antenna array with two-dimensional beam-scanning capability is presented in this paper. The design procedure is based on the continuous transverse stub (CTS) technology and the use of ferroelectric material. With the application of a low-loss ferroelectric material barium strontium titanium oxide with 40% oxide III, beam-scan capability from -60/spl deg/ to 60/spl deg/ was achieved. The tradeoffs in selecting the ferroelectric material and between losses and bias voltage in the CTS design were also examined. Furthermore, it was found necessary to adjust the dimensions of the radiating stubs, as well as the connecting sections of the feed waveguide so as to eliminate reflections between the stubs and, hence, maintain the desirable radiation pattern. It is shown that the use of an average height for the feed waveguide will result in deterioration in the radiation pattern.

The use of ferroelectric material for increasing the sensitivity of EPR spectrometers

To increase the sensitivity of the EPR spectrometers, the use of ferroelectric material (considered as additional resonator) is proposed. This new technique is examined on CW EPR spectrometer RE-1307 and on home-built Pulse EPR spectrometer, both at X-band. When ferroelectric resonator made from KTaO3 is used, signal-to-noise ratio in CW experiments is increased by factor of 10, while in electron spin echo experiment the incident power may be reduced by factor of 50 to obtain the same power on the sample. Frequency values are calculated for rectangular and cylindrical ferroelectric resonators.