Piezoelectrics and Ferroelectrics

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According to the literature, the materials below present or are predicted to present the properties of piezoelectricity and/or ferroelectricity in the form of thin films.

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MoS2          MoSe2          WS2          WSe2          SnSe          SnS

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GeSe           GeS               AlSb          GaP            GaAs          GaSb

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InP             InAs              InSb          CrSe2         CrTe2         CaO

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CdO            ZnO              InN           In2Se3        BaTiO3

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Piezoelectricity is the property that certain materials have of generating a difference in electrical potential at their ends in response to an applied mechanical stress (deformation) or, conversely, of varying their physical dimensions in response to an applied electrical voltage. This property normally appears in materials that have a crystalline structure without central symmetry, which induces the appearance of electrical polarization along a certain direction. Crystalline materials are divided into 32 crystallographic groups, among which 21 do not present central symmetry and originate piezoelectricity with the exception of group 432. They are 1, 2, m, 222, 2mm, 3, 32, 3m, 4, 422, 4mm, 2m, 6, 622, 6mm, 2m, 23 and 3m [1].

The most commonly used materials in the manufacture of piezoelectric devices are:

- SiO2 (quartz)

- PZT (Lead zirconate titanate - Pb(ZrxTi1-x)O3 )

- BaTiO3 (Barium titanate)

- BiFeO3 (Bismuth Ferrite)

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Ferroelectricity is a subgroup of piezoelectricity, in which certain materials have a spontaneous electrical polarization that can be reversed by the application of an external electric field. Thus, all ferroelectric materials are also piezoelectric, however with the additional property that their natural electrical polarization is reversible.

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​[1] https://dictionary.iucr.org/Piezoelectricity

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​​Al2O3 (alumina)

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• Anti-reflective layer for improving solar cells.

• Minimize leakage current and maximize the dielectric constant of SrTiO3-based capacitors with metal-insulator-metal (MIM) structure.

• Used as the "bottom gate" of a thin film transistor (TFT).

• Used as a protective layer for Si photocathodes in photoelectrochemical cells for H2 production.

• Improvement of the sensitivity and stability of the Raman technique known as "Surface-enhanced Raman scattering (SERS)".

• Application in CMOS logic and Flash memories.

• Transparent and water-repellent surfaces.

• Used to improve the properties of flexible electronic devices.

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CoAl2O4 (cobalt aluminate)

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• It is used in various technological applications, such as high-density magnetic recording, microwave devices, magnetic fluids, heterogeneous catalysis, absorbent materials and industrial pigments.

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ZnAl2O4 (zinc aluminate)

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• Widely used as a catalyst in various gaseous reactions and has great potential for photocatalytic degradation applications.

 

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BaTiO3 + CoFe2O4 (Barium titanate–cobalt ferrite composite)

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• Two-phase multiferroic system used as an alternative to single-phase multiferroics. This system arose from the search for materials that presented a stronger coupling between their ferroic orders (e.g., ferromagnetism and ferroelectricity), since in single-phase materials this coupling is generally very weak. Therefore, a new multiferroic system can be achieved by combining a ferroelectric phase (BaTiO3 - perovskite) with a ferrimagnetic phase (CoFe2O4 - spinel).

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ZnO (zinc oxide)

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• Due to its wide energy gap (3.37 eV), it has great potential for optoelectronic applications such as light-emitting diode (LED), being an excellent candidate to replace GaN.

• Its high visible transmittance associated with its good electrical properties (especially when doped with aluminum, forming AZO), make it a potential replacement for ITO in applications such as transparent conducting oxides (TCO).

• It can be easily doped with transition metals for Spintronics applications.

• It presents good stability to high-energy radiation and chemical wear, which allows applications in the aerospace industry.

• As it is an excellent absorber of ultraviolet radiation, it can be used as a protective layer for lenses, devices and polymers.

• It has great potential for applications such as thin-film transparent transistors (TTFT).

• It presents very interesting properties of resistive switching, allowing the study for applications in resistive random access memories (RRAM) and thin film varistors.

• It has a piezoelectric response (along the crystallographic c axis) that is quite appreciable for applications such as piezoelectric devices.

• When doped with aluminum, it can be used in infrared radiation blocking windows in energy saving applications.

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TiO2 (titanium dioxide)

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• It is a semiconductor with a wide band gap that is transparent to visible light and has excellent optical transmittance.

• Because it has a high refractive index and good insulating properties, it is widely used as a protective layer for integrated circuits and for manufacturing optical elements.

• Photo-voltaic cells.

• Anti-reflective surfaces.

• Gas sensors.

• Electrochromic displays.

• Planar waveguides.

• Its high dielectric constant allows it to be presented as an alternative to silicon dioxide as a dielectric layer in memories and logic devices.

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YSZ (yttria-stabilized zirconia - (ZrO2)1 – x(Y2O3)x)

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• The addition of Y2O3 to ZrO2 causes oxygen vacancies to appear, making the YSZ compound a good ionic conductor (O2-). This enables applications such as solid oxide fuel cell (SOFC).

• Due to its hardness and chemical inertness, it is widely used in bone and tooth implants.

• Due to its refractory property, it is widely used as a thermal barrier in jet engines and combustion turbines.

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​SrTiO3 (strontium titanate)

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• In microwave adjustable capacitors.

• In current flat panel displays, such as LCD, and in future field emission displays (FEDs).

• Devices for microwave applications.

• PTC thermistors.

• Varistors.

• Thermometers insensitive to magnetic fields.

• Ultra-low temperature scanning microscopes.

• Infrared pyroelectric detectors.​

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​BaTiO3 (barium titanate)

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• It is the most widely used material as a ferroelectric and one of the most important in dielectric multilayer applications.

• Because it presents the photorefractive effect, it is very interesting for applications in nonlinear optics.

• It has an appreciable piezoelectric property.

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BaSrTiO3 (barium-strontium titanate)

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• It is one of the most promising candidates for applications as Metal-Insulator-Metal (MIM) capacitor for dynamic random access memory (DRAM) as it exhibits high dielectric constant, high dielectric strength, low dielectric loss and good thermal stability. Therefore, it has a lot of potential to replace SiO2 in dielectric applications.