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Application of AFM for Analyzing the Microstructure of Ferroelectric Polymer as an Energy Material
Published in Cai Shen, Atomic Force Microscopy for Energy Research, 2022
Ferroelectric materials are special types of functional materials with a spontaneous electric polarization that can be reversed by the application of an external electric field in opposite direction. This unique switchable polarization endows the materials a broad range of applications including capacitors, non-volatile memories, oscillators, and filters. While the most important function of ferroelectrics may be their piezoelectricity, namely, the ability for electro-mechanical energy conversion owing to the lack of inversion symmetry, which makes the materials and their applications closely linked to energy, an issue of increasing priority for human. In addition to the traditional piezoelectric transducers, actuators, and force sensors, various emerging devices like energy harvesters, nanogenerators, electro-optic systems, and catalysts are getting global attention.1
A universal memory that never runs out of steam
Published in Rajesh Singh, Anita Gehlot, Intelligent Circuits and Systems, 2021
Urvashi Sharma, Sachin Mishra, Gulshan Kumar, Reji Thomas
Some of the dielectric materials, ferroelectric materials are also used in non-volatile memories. The perovskite materials, PbTiXZr1xO3 (PZT) and layered strontium-bismuth-tantalite alloy (SBT) are the ferroelectric choice for this so far [5]. This non-volatile memory is termed as ferroelectric RAM (Fe-RAM). The cell construction is the same as DRAM (1T-1C) with a non-linear ferroelectric capacitor instead of a linear dielectric capacitor [9]. Fe-RAMs are based on remnant polarization at zero applied electric field in ferroelectric crystal. These have the ability to switch polarization (±Pr) with an external electric field [5]. It has the non-volatility of Flash, but having demerits of lower density (< DRAM) and high manufacturing cost (~SRAM). Fe-RAM is used in local area network (LAN) bypass, advanced metering, automotive shift-by-wire, process control in industries, navigation, solid-state drive (SSD), gaming, motion control etc. The widely investigated ferroelectric-memories possess low voltage to 0.9 V, endurance more than 1013 write/read cycles, write speed of 100 ns at low voltage with retention of about 10 years [19]. However, the low density is the hindrance in replacing Flash, EEPROM, DRAM and SRAM to realize a “Universal Memory” with ferroelectric and this aspect is discussed in the following section.
Electronic Properties of Perovskite Oxides
Published in Gibin George, Sivasankara Rao Ede, Zhiping Luo, Fundamentals of Perovskite Oxides, 2020
Gibin George, Sivasankara Rao Ede, Zhiping Luo
Ferroelectric materials undergo spontaneous polarization under an external electric field, and the same can be reversed only by the application of an external electric field in the opposite direction. In ferroelectric materials, all the domains are aligned in the same direction; therefore, strong polarizations appear in the direction of the electric field. Similar to ferromagnets, residual electric polarizations remain even after the electric field is removed. The hysteresis loop of ferroelectric polarization against the external field is shown in Figure 6.20. Many perovskite materials exhibit ferroelectricity below a phase transformation temperature, called the Curie temperature Tc, and are paraelectric above this temperature. A representative transition of paraelectric to ferroelectric behavior in perovskite materials is shown in Figure 6.21.
Recent advances in neuromorphic transistors for artificial perception applications
Published in Science and Technology of Advanced Materials, 2023
Figure 2(d) shows a schematic of FeFET. FeFETs have broad application prospects in artificial synapses due to their easy programming, large switching ratio, low power consumption and non-volatile characteristics. For FeFETs, the ferroelectric dielectric layer is the key to realize the synaptic function. The working principle of FeFETs is as follows. Ferroelectric materials is capable of spontaneous polarization. While the gate voltage will make it reverse in the direction of spontaneous polarization. Furthermore, by controlling the amplitude and time of the gate biases, the polarization inversion can also be obtained accurately, demonstrating non-volatile characteristics [72]. Based on this non-volatile modulation, FeFETs can be adopted to simulate the plasticity of biological synapses [61,73].
Temperature-dependent model for ferroelectrics embedded into two-dimensional polygonal finite element framework
Published in Mechanics of Advanced Materials and Structures, 2023
Dheeraj Kailas Valecha, Jayabal K, Amirtham Rajagopal
In the paraelectric state above the Curie temperature, ferroelectric ceramics have a higher symmetry cubic crystal structure, which inhibits the underlying unit cells from spontaneously polarizing. When a ferroelectric material cools below the transition temperature, it develops a less symmetric crystal structure, which leads to charge center separation and spontaneous polarization within the unit cell. Additionally, in connection to the cubic state, the unit cell experiences spontaneous pressure. While the state of lower crystal symmetry (tetragonal, rhombohedral, or orthorhombic) of ferroelectric ceramics can vary, depending upon their constituents, we will discuss only a rhombohedral and tetragonal phase in this paper. There are up to six different types of domain orientations that can be applied to a single ferroelectric crystal, and a domain is a cluster of unit cells with equal polarization orientation. The sharp interface that separates distinct domains is referred to as a domain wall. Since individual domain microscopic strain and polarization contributions amount to zero, as averaged in an integral or rather volume way, ferroelectrics show no net macroscopic polarization and strain in a depoled state. Consequently, the electromechanical response of ferroelectrics in this depoled state is not immediately coupled. This means that the material essentially acts as an elastic or an electric body under external electromechanical loads.
The electrocaloric effect in BaTiO3:Eu ceramics determined by an indirect method
Published in Phase Transitions, 2021
Przemysław Gwizd, Dorota Sitko, Irena Jankowska-Sumara, Magdalena Krupska-Klimczak
Barium titanate BaTiO3 (BT) maybe the most explored ferroelectric material possessing many useful properties. Moreover, BaTiO3 belongs to lead-free ferroelectric materials which are important for ecologic reasons. It possesses relatively good piezoelectric properties with a direct piezoelectric coefficient d33 = 191 pC/N and a large electromechanical coupling factor kP of up to 0.36% [14,15]. Donor-activated BT ceramics have been widely used in electronic devices as high-permittivity capacitors and positive temperature coefficients of resistivity devices [16–20]. Moya et al. [21] measured the EC effect of single-crystalline BaTiO3 samples and reported a temperature change of around 1.0 K. In [12], a giant electrocaloric effect (ΔT∼4 K) was reported in single crystals of BT, however, it appeared to be unstable to thermal cycles and alternating electric fields. In the same work, better repeatability and reliability were observed for BT ceramics, although with lower ΔT values. Yang-Bin Ma [22] studied the influence of non-switchable defect dipoles on the existence of both positive and negative ECE in acceptor doped BaTiO3.