Perspective Cite This: Chem. Mater. 2018, 30, 8718−8726
pubs.acs.org/cm
Applications of Piezoelectrics: Old and New† Alicia María Manjón-Sanz‡,§ and Michelle R. Dolgos*,‡,∥ ‡
Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States CELLS-ALBA Synchrotron Light Facility, Cerdanyola del Valles, 08290 Barcelona, Spain ∥ Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4
Chem. Mater. 2018.30:8718-8726. Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/19/19. For personal use only.
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ABSTRACT: Piezoelectric materials convert between electrical and mechanical energy and vice versa. They can be found in many different electronic applications from gas sensors to micromotors. While piezoelectrics were first discovered in the late 1800s, scientists and engineers are still developing new applications to help advance technology. This perspective summarizes the history of piezoelectric materials and describes interesting applications of the past, present, and future. It also highlights the challenges in fundamental science and how chemists can make significant contributions to the field.
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INTRODUCTION Piezoelectric materials convert electrical energy to mechanical energy and vice versa, resulting in observed properties that are electromechanically coupled. When a piezoelectric material is deformed, that mechanical energy is transformed to electrical energy, which is known as the direct piezoelectric effect (Figure 1, top). When the reverse occurs and an electric field is applied, the material physically deforms, resulting in the converse piezoelectric effect (Figure 1, bottom). Therefore, piezoelectric materials can be used in both sensor and actuator applications. The magnitude of the piezoelectric response is often expressed as the longitudinal piezoelectric coefficient, d33. When measuring the direct piezoelectric effect, d33 is the polarization generated per unit of mechanical stress, where the field and stress are along the same direction. In the converse effect, d33 is the induced mechanical strain per unit of electric field applied, with the field and stress also in the same direction. Another measure of effectiveness of a piezoelectric is called the electromechanical coupling factor, k. This value expresses the efficiency of conversion from mechanical to electrical energy or vice versa. The direct piezoelectric effect was first demonstrated in 1880 by brothers Pierre and Jacques Curie.5 They applied mechanical stress to a variety of single crystals including tourmaline, quartz, topaz, and Rochelle salt.6 The stress applied to the crystals resulted in a measurable surface charge. However, they did not initially show it was also possible to produce an electric field induced strain. The following year, mathematician Gabriel Lippman predicted the converse piezoelectric effect which was quickly confirmed afterward by the Curie brothers.7 Over the next 25 years, the theory of piezoelectricity was developed significantly, but not much progress was made
toward its use. The watershed moment in applications did not occur until 1917, during World War I, when Paul Langevin developed a quartz sonar device for ultrasonic submarine detectors.8 This successful use of piezoelectric materials paved the way for the intense and rapid advancement of many different kinds of piezoelectric devices including microphone components, accelerometers, phonographs, signal frequency filters, and ultrasonic transducers. During World War II and the two decades following, research in piezoelectrics focused on finding new materials and improving the quality of devices. The classical piezoelectric material barium titanate, BaTiO3, and the current industry standard lead zirconium titanate, Pb(Zr,Ti)O3 (PZT), were discovered during this time.9 PZT is a solid solution where there is an enhanced piezoelectric effect in a narrow composition range called the morphotropic phase boundary (MPB).9 PZT-based compositions within the MPB have shown the highest piezoelectric response, d33, to date. During this time period, device performance was improved because scientists finally understood how the crystal structure was related to the electromechanical coupling, and they also found that doping these materials can greatly enhance the piezoelectric response. From this point, new high-tech applications developed at an impressive rate. These applications included more powerful sonar, ignition systems, snap action relays, sensitive microphones, circuit elements, and ceramic audio tone transducers. Starting in the 1990s and continuing today, fundamental research began to focus on understanding the origins of the piezoelectric mechanism at the MPB, 10−13 developing advanced processing techniques,14,15 investigating the effect Received: August 3, 2018 Revised: November 20, 2018 Published: November 26, 2018
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This Perspective is part of the Up-and-Coming series. © 2018 American Chemical Society
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Figure 1. Schematic depicting the mechanism for direct (top) and converse (bottom) piezoelectricity.
of dopants on physical properties,16−19 and synthesizing leadfree piezoelectrics to replace the industry favorite PZT.12,20−23 In addition, significant progress was made to process ceramics for high volume markets. Today there is additional focus on synthesizing high temperature materials,24 moving lead-free materials toward applications,23,25−27 developing high tech applications,28−32 and improving the quality of thin film devices.33−36 Most modern piezoelectric materials have the perovskite crystal structure (Figure 2). The perovskite has the ABO3
material to display piezoelectric properties.37 They must be noncentrosymmetric, which means there is no center of symmetry. Of the 32 crystal classes, 20 are noncentrosymmetric and therefore exhibit piezoelectricity. Ten of those crystal classes have a unique polar axis, which results in the spontaneous polarization upon the application of an electric field, resulting in pyroelectric behavior. If the polar axis switches with the direction of the field, then the material is ferroelectric as well. Most of the well-known perovskite piezoelectric materials crystallize in these space groups and therefore display ferroelectric, pyroelectric, and piezoelectric properties. It can easily go unnoticed how prevalent piezoelectric materials are in everyday electronic devices. To help convey the widespread use of piezoelectrics, it is important to understand that the market for devices was valued at $21.60 billion USD in 201538 and is expected to grow to $31.33 billion USD by 2022.39 Many chemists are frequently exposed to popular topics in materials chemistry, such as photovoltaics, batteries, fuel cells, and nanomaterials, but are only briefly introduced to the concept of piezoelectricity in a solid state chemistry course. To that end, this paper will highlight common examples of current applications as well as more forward-looking technology under development. It will also include the fundamental science that still needs to be addressed, the community’s fractured view on lead-free materials, and the role of a chemist in this highly applied field.
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Figure 2. Perovskite structure with A-sites (green), B-sites (blue), and anion (red). This picture represents slightly more than one unit cell to show the coordination environments of both cations.
APPLICATIONS UTILIZING THE DIRECT PIEZOELECTRIC EFFECT Sensor applications take advantage of the direct piezoelectric effect where mechanical energy is converted to electrical energy. Piezoelectric sensors can detect changes in pressure, acceleration, force, etc. When a strain is applied to the sensing component, it becomes polarized due to the electrical dipole moment. Any slight modification of the stress results in a polarization change from the rearrangement of the dipole moment. This causes a measurable difference in the electrical potential across the device, thus making piezoelectrics sensitive to very small changes. While the following examples are not
chemical formula. The A-cation is typically a large electropositive cation which is found in an A−O polyhedral unit with a coordination number of 12. The B-cation is smaller, usually a transition metal in a BO6 octahedra coordination environment. Perovskites have the most compositionally flexible crystal structure that can easily be tuned for specific applications, so it is not very surprising that most piezoelectrics have this structure. There are certain structural requirements for a 8719
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communication, to provide useful information about the state of the environment of interest.41 Piezoelectrics can be used in medical, neural, environmental, chemical, infrared, radio frequency identification (RFID), and mobile phone sensors that are connected to the IoT. One specific example that receives significant attention is piezoelectric sensors for structural health monitoring. This application allows for early detection of defects in beams, plates, and pipes, so that repairs can be made before significant damage occurs. Current research in this area focuses on using ceramic/polymer composites and piezoelectric nanostructures including nanowires, nanoplates, nanofibers, and nanoparticles.42−45 These materials are thought to have superior properties and are less brittle than single phase ceramics. In addition, for all sensor applications in the IoT, work must be done to reduce the cost of sensors, lower their power consumption, and discover new materials that can handle exposure to harsh environments. Energy Harvesting. The direct piezoelectric effect can be exploited to harvest energy via repetitive vibrational movements. These vibrations are normally wasted energy, but it can be converted to electrical energy through a piezoelectric device and then used to charge a battery or supercapacitor or directly power a system. One obvious place that wasted energy can be harvested from is the repetitive motions of the body. Table 1
comprehensive of all possible sensor applications, they highlight several common uses as well as some interesting technologies of the future. Automobile Industry. As driving technology and safety improves, piezoelectric sensors are increasingly incorporated into vehicles. PZT is currently used in devices for knock sensors, tire pressure monitors, airbag and seatbelt sensors, gyroscopes, accelerometers, and engine fluid detection. In each of these applications, vibrations or other types of mechanical pressure on the sensor result in an electric field, which is then relayed to the vehicle’s computer. In the future, as autonomous cars develop, the need for piezoelectric sensors in automated driving features will increase. In most cases, the applications will not change, but new sensors must be developed to deal with more fully autonomous vehicles to increase safety and efficiency.40 Medical Technology. In the medical industry, piezoelectric materials are commonly found in ultrasound devices. Ultrasound scanners use a piezoelectric transducer (usually PZT, Pb(Mg,Nb)O3−PbTiO3, or polyvinylidene fluoride) that utilizes the converse piezoelectric effect to send out sound vibrations that are reflected by muscles, organs, etc. The device also uses the direct piezoelectric effect to detect the reflected sound which is then displayed as an image to be analyzed. This technology now allows doctors to view highly detailed 3D images (Figure 3) so they no longer need to rely on less
Table 1. Available Energy Generated by the Human Body during One Daya
a
activity
power (W)
activity
power (W)
foot strike ankle motion knee motion hip motion
2−20 ∼33.4 ∼36.4 ∼38
blood circulation respiration elbow motion shoulder motion
∼0.9 ∼1.0 ∼2.1 ∼2.2
Reprinted with permission from ref 1. Copyright 2018 Elsevier.
shows the energy available from different motions of the human body throughout the day.1 One example where this technology is actively being used is in the harnessing of energy from footsteps. Piezoelectric tiles have been placed on a dance floor (Surya in London)46 and train station floors (Tokyo)47 where the output energy is stored in a battery and used to power some of the lighting at each facility. While each step only generates ∼0.1 W of power, the use of these tiles in high traffic areas can make a significant impact. As new high performing materials are discovered and devices become more efficient, this application will become more prevalent in society. In the future, energy harvesting will play a critical role in the Internet of Things as every sensor will need a power source. Sensors in remote locations cannot rely on batteries, which eventually discharge. The unlimited supply of power from piezoelectric energy harvesters could allow the sensor to function continuously for the duration of its life.
Figure 3. Example of an image taken with a three-dimensional ultrasound transducer using piezoelectric technology. 3D image courtesy of Mindray.
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reliable 2D pictures to make a diagnosis or guide them during surgery. Other sensor applications in the medical field include electronic stethoscopes, hearing aids, flow meters to monitor vascular health, and both external and internal sensors for health status monitoring. Internet of Things (IoT). As society moves toward integrating the digital and physical world via the Internet of Things (IoT), piezoelectric materials and devices are becoming increasingly important. An IoT “smart” device uses a sensor to perceive the world around it. The data is collected, stored, processed, and shared intelligently, usually through wireless
APPLICATIONS UTILIZING THE CONVERSE PIEZOELECTRIC EFFECT In the case of the converse piezoelectric effect, electrical energy is transformed to mechanical energy. The lattice expands when the field is applied in the same direction as the dipole direction, while the lattice contracts when the field is applied in the opposite direction as the dipole. The mechanical displacement produced from a piezoelectric element is very small, ranging from 1 to 100 μm. However, piezoelectric actuators do not 8720
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Noise/Vibration Reduction. In the modern world, significant noises and vibrations are produced because of traffic, industrial production, and construction, which causes concerns for human health, industrial safety, and the environment.52−55 Consequently, damping materials are becoming increasingly important. A phenomenon called the piezo-damping effect transforms the external mechanical energy from noise into electrical energy which is dissipated as heat energy. The piezo-damping device uses both the direct and the converse effect (similar to medical ultrasound devices). The actuator, a piezoceramic, is used for the active vibration dampening while the sensor, a piezopolymer, is used to measure the vibrations of the structure.56 The resultant vibration measurement then controls the voltage applied to the actuator to minimize the unwanted vibrations. While this concept, in theory, seems effective, its use is limited because of complications involving the integration of the actuator, sensor, and power supply and control. However, recently some piezodamping composites have been investigated with promising results achieved.57−61 Perhaps this piezoelectric application will become more prominent in the future.
have a complex design, which allows them to quickly generate forces under low applied voltages. The section below focuses on a few of the many applications in today’s society that utilize the converse piezoelectric effect. Acoustical Devices. Piezoelectric materials can be used to convert electric fields to mechanical vibrations that provide sound in many applications where a speaker is found. Piezoelectric speakers are often found in technology such as cell phones, microphones, ear buds, sound-producing toys, and musical greeting cards.48 Piezoelectric speakers are advantageous over conventional speakers because they are small in size, immune to changes from magnetic fields, and only require a low power input.49 The converse piezoelectric effect is also used to generate acoustic signals for sonar devices, which is one of the oldest applications of piezoelectric materials. Sonar technology can both generate (converse effect) and detect (direct effect) acoustical waves. To create sound waves, a piezoelectric disc vibrates at ultrasound frequencies upon application of an electric field. Sonar can be used for underwater imaging and underwater communication in a wide variety of military, industrial, and scientific applications. Just a few examples of sonar applications include underwater communication, fish finders, and ocean surveillance. Piezoelectric Motors. Piezoelectric motors can generate unlimited rotary or linear movements of up to 100 μm and can offer high precision positioning on the nanometer scale. These two characteristics make them appropriate for long stroke micropositioning applications. Piezoelectric motors can be divided into three categories based on the different drive and functional properties for producing unlimited rotatory or linear movement: (1) resonance drive or ultrasonic motors, (2) inertia-drives, and (3) stepping piezo actuators.50 This technology plays an important role in the world of robotics. For example, motors on the millimeter scale using MEMs (microelectrical−mechanical systems) can generate the flying or walking motion of bug-like robots (Figure 4). The
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LEAD-FREE PIEZOELECTRICS As mentioned previously, Pb(Zr,Ti)O3 (PZT) is the industry standard piezoelectric material and shows outstanding properties such as a high piezoelectric response (d33 ∼ 200−600 pC/ N) and a good electromechanical coupling factor (kp ∼ 0.67)62 and can be easily modified by doping for tailored use in a large number of applications. While lead is restricted or banned in most applications because of its toxicity, it is still regularly used in piezoelectric devices because there is no good substitute for PZT. There have been many worldwide discussions about the removal of lead from electronics, but governing documents such as the EUs Restriction of Hazardous Substances (RoHS) continues to make an exemption for PZT. While many scientists in the field are working to find alternative materials, others feel that PZT should continue to be used in applications. The piezoelectric community is in agreement that it will take more than one composition to replace PZT as there has been tremendous difficulty in finding one material with the same diverse properties found in PZT.63 This struggle makes the transition away from PZT less appealing to industry, who currently use a single standard process to make devices for many different applications. The complications from using different materials for different applications will increase the complexity of manufacturing and likely drive up the cost. On the other hand, some scientists believe that it is only a matter of time before the RoHS exemptions expire, forcing a move to lead-free materials, so research in this area is very much alive and strong. Within the piezoelectric community, lively discussion focuses on whether lead-free materials are actually safer for the environment compared to PZT. A collaboration between several groups in the United Kingdom are working to quantify the environmental impact of PZT and its lead-free counterparts via life cycle analysis to take a more measured approach to the problem. They recently published several papers comparing PZT to potassium sodium niobate, K0.5Na0.5NbO3 (KNN).4,64 KNN is a well-studied lead-free piezoelectric that has potential to replace PZT as it is also possible to tune the piezoelectric response or increase the Curie temperature (∼300−450 °C) of KNN through doping.65 These assessment studies examined 16 sustainability metrics and show that there
Figure 4. PZT MEMs actuator used to flap the wings of a small-scale robotic bug. Figure reproduced with permission from ref 2. Copyright 2012 Materials Research Society.
piezoelectric material deforms when an electric current is applied and generates oscillations that can be translated into wings flapping or a forward crawl. Bug-like robots have many characteristics of real insects, but they are obviously not limited by evolution and survival needs. Therefore, small robot bugs equipped with cameras and chemical sensors can be used to explore new places such as Mars and hard to reach territories like cracks in rocks.51 8721
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Figure 5. Environmental impacts of PZT versus KNN for various sustainability metrics as determined by Ibn-Mohammed et al. GHG stands for greenhouse gas emissions, MSETP stands for marine sediment ecotoxicity, HTP stands for human toxicity, and FAETP stands for freshwater sediment ecotoxicity. Figure reproduced with permission from ref 4. Copyright 2017 Materials Research Society.
design, (2) solution processing of thin films, and (3) structural determinations of bulk ceramic materials. Synthesis of New Materials. The discovery of new piezoelectrics is increasingly important for both the push toward lead-free materials and the desire for advancing new technologies. While some argue that PZT is not that hazardous for the environment, it still has its physical limitations. For example, it cannot operate above temperatures of ∼150 °C,9 which severely restricts its use in high temperature applications in the automobile and aerospace industries. It also suffers from stability issues due to fatigue, and it can only create small strains of ∼0.1−0.3%.66−68 In addition, one of the more forward-looking applications for piezoelectrics is in vivo biomedical devices in which PZT cannot be used because lead poisoning can cause severe damage to the human body.69 The necessity for new piezoelectric materials clearly exists, but there is currently no substitute for PZT, despite decades of effort. Chemists are in a prime position to discover and synthesize new materials that can replace PZT. As mentioned previously, most scientists in the piezoelectric community agree a variety of different materials are needed to substitute for PZT. Thus far, it has been difficult to find a single composition with the same diverse characteristics as PZT, which can be readily doped to tune the electromechanical properties.63 The standard synthesis method for bulk ceramics is the solid
is a high environmental cost for KNN during the earliest stages of its life cycle, while the environmental damage caused by PZT occurs during use and at end-of-life disposal. In many of the metrics used, KNN appears to be significantly worse for the environment as shown in Figure 5. The main reason is that niobium oxide, Nb2O5, one of the starting materials used in KNN production, has an incredibly high carbon footprint.4 The extraction of Nb2O5 has significant impact on the air and ground quality as well as surrounding habitats. The mining of niobium results in harmful waste such as heavy metals, radioactive materials, and acids. Processing of niobium oxide after extraction and as used during synthesis of KNN also has a much higher energy input than any of the precursors in PZT.64 This interesting study shows that while there is a push to remove lead from piezoelectric devices, further studies must be done and much care needs to be taken when considering the alternatives.
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THE ROLE OF A CHEMIST IN FUTURE RESEARCH Few of the scientists performing research in the piezoelectric community are chemists. It is a field dominated by materials scientists/engineers, but there are several challenges where the skills and viewpoints of a chemist could quickly help advance our fundamental understanding of piezoelectric materials. Three specific examples of research problems where a chemist’s skills are essential include (1) synthesis and materials 8722
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systems are notoriously difficult to determine correctly because of their local distortions. Materials with highly polarizable atoms are known to possess a local, short-range structure that is different from their average, long-range structure. PZT has local distortions within the morphotropic phase boundary (MPB) where there is a sharp increase in piezoelectric response. These distortions and their relationship to the average structure and physical properties have been characterized in an incredible amount of detail.75−89 Structural studies of PZT’s lead-free counterparts often lack an in-depth, systematic approach that is needed to truly understand the performance gap between PZT and the lead-free piezoelectric systems. As a result, the local atomic arrangement of many lead-free systems remains elusive. Studying local order (or disorder) through diffraction (neutron, X-ray, electron) and microscopy techniques will lead to a greater understanding of the enhanced piezoelectric response at the MPB as well as a determination of the fundamental differences between PZT and its lead-free alternatives. Another important technique for studying local scale structural distortions is the pair distribution function method. The pair distribution function provides access to short-, medium-, and long-range ordering. This information is particularly important in piezoelectrics as polarizable atoms often drive local distortions from the average structure, and understanding these short-range interactions is important for unlocking the mechanisms that lead to piezoelectricity. It is also important to look at the structure under operating conditions. In situ electric field diffraction has been utilized to make important discoveries about the structure−property relationships in piezoelectric materials,90−106 but we have only begun to scratch the surface of the work needed in this area. Many materials chemists, in particular solid state chemists, have expertise in crystallography and structural characterization using a variety of techniques. There is plenty of space to explore in this area, and their input is welcome (and needed) to gain greater insight into the structural intricacies of piezoelectrics.
state technique where starting materials in the powder oxide and/or carbonate form are mixed together, pressed into a pellet, and heated to form the target phase. This method is simple and usually leads to thermodynamically stable products. However, it can often result in inhomogeneous products, poor kinetic control, and loss of volatile starting materials during the reaction. It can also be difficult to find the correct conditions to form the thermodynamically stable phase. Chemists are well versed and highly skilled in alternative methods such as sol gel, hydrothermal, and microwave synthesis that have the potential to access metastable phases or phases that are unattainable via the traditional synthesis method. More chemists are needed in the field to perform exploratory synthesis that will result in new materials to be used in both current applications and in future applications that have not even been imagined yet. Solution Processed Thin Films. Thin films are becoming increasingly important as technology becomes smaller. However, large-scale commercial applications of some compositions can be limited due to current thin film deposition methods. Vapor deposition methods are energy intensive, cause problems with cation volatility, and can be difficult to scale up. Sol−gel deposition suffers from the issues of scaling, poor film quality, and air sensitivity. It also requires the use of carcinogenic or toxic organic solvents. However, a promising deposition method known as solution processing (spin-coating) via prompt inorganic condensation (PIC)70 (Figure 6) may be viable for the large-scale production of oxide
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Figure 6. Spin coating solution deposition steps using the prompt inorganic condensation technique. Reprinted with permission from from ref 3. Copyright 2015 Elsevier.
CONCLUSION Piezoelectrics are a prevalent and important type of material used in a variety of applications. While they were discovered over 100 years ago, scientists are still finding new ways to use them. Currently, a considerable focus among scientists is to move toward lead-free materials to reduce the impact on the environment. However, there are questions about whether these materials are actually better for the environment compared to PZT. Regardless of the results of the lead-free debate, there is still much work to be done to understand the fundamental science of piezoelectrics in both ceramics and thin films. Chemists are strongly encouraged to work on these challenges as their skill set will naturally lead to significant progress in the field. The future holds many opportunities where chemists can make substantial contributions to an exciting field with interesting challenges in both fundamental and applied chemistry.
thin films for electronic applications. This deposition method utilizes aqueous precursor solutions71−73 that are stable in air and only need moderate annealing temperatures for thin film formation. The resultant films display a lower surface roughness and fewer defects in dielectrics such as Al2O3, for example,74 but it has yet to be applied comprehensively to a wide variety of materials, including piezoelectrics. In relation to piezoelectrics, the PIC method has only been used to deposit LiNbO3 thin films.3 This study was a fundamental proof-of-concept investigation to understand how the polyoxometalate precursor, Li6[H2Nb6O19]·14H2O, transforms into the metal oxide, LiNbO3. Therefore, the research space is wide open for the development of the precursor solution chemistry. Chemists are ideally suited for this work as it requires expert knowledge, specifically in acid/ base chemistry, solubility, and metal−oxo clusters. The potential for chemists to use this novel technique to advance the fundamental understanding and practical applications of thin film piezoelectrics is incredibly exciting. Structural Determinations of Bulk Ceramic Materials. The crystal structures of both PZT and lead-free piezoelectric
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AUTHOR INFORMATION
Corresponding Author
*(M.R.D.) E-mail:
[email protected]. ORCID
Michelle R. Dolgos: 0000-0003-1969-8181 8723
DOI: 10.1021/acs.chemmater.8b03296 Chem. Mater. 2018, 30, 8718−8726
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(6) Mason, W. P. Piezoelectricity, its history and applications. J. Acoust. Soc. Am. 1981, 70, 1561−1566. (7) Curie, J.; Curie, P. Contractions et dilatations produites par des tensions electriques dans les cristaux hemiedres a faces inclinees. Comptes-rendus de l’Academie des Sciences 1881, 93, 1137−1140. (8) Manbachi, A.; Cobbold, R. S. C. Development and application of piezoelectric materials for ultrasound generation and detection. Ultrasound 2011, 19, 187−196. (9) Jaffe, B.; Cook, W. R.; Jaffe, H. Piezoelectric Ceramics; Academic Press Inc.: New York, NY, 1971. (10) Damjanovic, D. Contributions to the Piezoelectric Effect in Ferroelectric Single Crystals and Ceramics. J. Am. Ceram. Soc. 2005, 88, 2663−2676. (11) Bell, A. J. Factors influencing the piezoelectric behaviour of PZT and other ″morphotropic phase boundary″ piezoelectrics. J. Mater. Sci. 2006, 41, 13−25. (12) Guo, R.; Cross, L. E.; Park, S. E.; Noheda, B.; Cox, D. E.; Shirane, G. Origin of the high piezoelectric response in PbZr1‑xTixO3. Phys. Rev. Lett. 2000, 84, 5423−5425. (13) Fu, H. X.; Cohen, R. E. Polarization rotation mechanism for ultrahigh electromechanical response in single-crystal piezoelectrics. Nature 2000, 403, 281−283. (14) Guo, J.; Guo, H.; Baker, A.; Lanagan, M. T.; Kupp, E.; Messing, G. L.; Randall, C. A. Cold Sintering: A Paradigm Shirt for Processing and Integration of Ceramics. Angew. Chem., Int. Ed. 2016, 55, 11457− 11461. (15) Richerson, D. W. Modern Ceramics: Properties, Processing, and Use in Design, 3rd ed.; CRC Press, Taylor & Francis Group: Boca Raton, FL, 2006. (16) He, L. X.; Li, C. E. Effects of addition of MnO on piezoelectric properties of lead zirconate titanate. J. Mater. Sci. 2000, 35, 2477− 2480. (17) Nagata, H.; Takenaka, T. Additive effects on electrical properties of (Bi1/2Na1/2)TiO3 ferroelectric ceramics. J. Eur. Ceram. Soc. 2001, 21, 1299−1302. (18) Kamiya, T.; Suzuki, T.; Tsurumi, T.; Daimon, M. Effects of manganese addition on piezoelectric properties of Pb(Zr0.5Ti0.5)O3. Jpn. J. Appl. Phys. 1992, 31, 3058−3060. (19) Zhang, L. X.; Chen, W.; Ren, X. Large recoverable electrostrain in Mn-doped (Ba,Sr)TiO3 ceramics. Appl. Phys. Lett. 2004, 85, 5658− 5660. (20) Cross, L. E. Dielectric, Piezoelectric, and Ferroelectric Components. Am. Ceram. Soc. Bull. 1984, 63, 586−590. (21) Haun, M. J.; Furman, E.; Jang, S.-J.; Cross, L. E. Thermodynamic theory of lead zirconate-tianate solid solution systems. Ferroelectrics 1989, 99, 13−25. (22) Du, X.-h.; Zheng, J.; Belegundu, U.; Uchino, K. Crystal orientation dependence of piezoelectric properties of lead zirconante titanate near the morphotropic phase boundary. Appl. Phys. Lett. 1998, 72, 2421−2423. (23) Rodel, J.; Jo, W.; Seifert, K. T. P.; Anton, E.-M.; Granzow, T.; Damjanovic, D. Perspective on the Development of Lead-free Piezoceramics. J. Am. Ceram. Soc. 2009, 92, 1153−1177. (24) Zhou, Z.-Y.; Tao, C.; Dong, X.-L. Reserch Progress of Perovskite Layer Structured Piezoelectric Ceramics with Super High Curie Temperature. Wuji Cailiao Xuebao 2018, 33, 251−258. (25) Hong, C.-H.; Kim, H.-P.; Choi, B.-Y.; Han, H.-S.; Son, J. S.; Ahn, C. W.; Jo, W. Lead-free piezoceramics - Where to move on? J. Materiomics 2016, 2, 1−24. (26) Panda, P. K. Review: environmentally friendly lead-free piezoelectric materials. J. Mater. Sci. 2009, 44, 5049−5062. (27) Aksel, E.; Jones, J. L. Advances in Lead-Free Piezoelectric Materials for Sensors and Actuators. Sensors 2010, 10, 1935−1954. (28) Mori, T.; Priya, S. Materials for energy harvesting: At the forefront of a new wave. MRS Bull. 2018, 43, 176−180. (29) Gullapalli, H.; Vemuru, V. S. M.; Kumar, A.; Botello-Mendez, A.; Vajtai, R.; Terrones, M.; Nagarajaiah, S.; Ajayan, P. M. Flexible Piezoelectric ZnO-Paper Nanocomposite Strain Sensor. Small 2010, 6, 1641−1646.
The authors declare no competing financial interest. Biographies Alicia Manjón Sanz received her B.Sc. in Chemistry from the Universidad Autónoma de Madrid (Spain). She obtained a Marie Curie Early Stage Researcher fellowship and joined the Rosseinsky group at the University of Liverpool (UK) from where she received her Ph.D. Alicia spent also half of her Ph.D. in the Takata laboratory at the SPring-8 synchrotron (Japan), where she studied the structure of bismuth based electroceramic perovskites using the maximum entropy method−Rietveld method. She then did a postdoc in the Dolgos group at Oregon State University (US). Currently, she works at the ALBA Synchrotron Light Facility (Spain) at the Materials Science and Powder Diffraction beamline. Her research interests lie in synthesis and elucidation of the structure−property relationships in advanced functional materials. Michelle Dolgos is an Assistant Professor at the University of Calgary (since November 2018). She obtained her B.Sc. in Chemistry from Hillsdale College (2002) in Michigan and her M.Sc. in Chemistry from the University of Tennessee (2005). She received a Ph.D. in Chemistry from The Ohio State University (2009) where she worked with Professor Pat Woodward studying the structure−property relationships of complex oxides and oxyfluorides. Michelle spent three years at the University of Liverpool as a postdoctoral research associate with Professor Matt Rosseinsky where her research focused on the synthesis and characterization of novel lead-free piezoelectric materials. Following her postdoc, Michelle obtained a faculty position as an Assistant Professor at Oregon State University (2013-2018) before moving to Calgary. Her research interests span a broad range of topics, but she specifically works in the following three areas: (1) synthesis and characterization of novel electronic materials, (2) development of new processing techniques for thin films, and (3) structural studies of amorphous and nanocrystalline materials for electronic applications. In each case, the ultimate goal is to rationally design and tune new materials with the desired properties for specific applications.
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ACKNOWLEDGMENTS M. Dolgos and A. Manjón-Sanz would like to thank the National Science Foundation for support under Grant No. DMR-1606909. They would also like to thank Charles Culbertson for designing and creating Figure 1,,.
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