High-performance Piezoelectric Materials Research Articles

AlScN based MEMS quasi-static mirror matrix with large tilting angle and high linearity

This paper presents a piezoelectrically (AlScN) driven 3 × 3 quasi-static mirror matrix, where each MEMS mirror utilizes a three-level-construction comprising a mirror plate (diameter = 0.8 mm), a pillar and four AlScN actuators hidden beneath the mirror plate, reducing the chip size to 1.1 × 1.3 mm2. AlScN as a high performance piezoelectric material is used to deliver large force enabling a mechanical tilting angle of ±14° at 150 VDC, in addition to great linearity, repeatability and long-term stability. For realizing the 3D construction three wafers for mirror plate, actuators and a TSV wafer for the vertical electrical contacts are applied. While first demonstrators have been manufactured by a chip-level hybrid assembly to mount the mirror plates onto the actuators, a BEOL triple-wafer-bonding process has been developed to integrate the mirror plates onto the actuators and TSV wafer. This paper will show the design and process efforts for improving the mechanical behavior of the MEMS mirrors, the process effort and current result of triple-wafer-bonding. It concludes by discussing the technological achievements, challenges and outlook for improved performance due to the material development of AlScN.

Piezoelectric Nanocellulose Thin Film with Large-Scale Vertical Crystal Alignment.

Cellulosic materials are attractive candidates for nature piezoelectrics. Vertically aligned cellulose nanocrystal (CNC) films are expected to show strong piezoelectricity as the largest dipole moment in CNCs exists along the cellulose chain. In this work, we adapted the confinement cell technology that was used to fabricate colloidal opal structures to align CNC rods vertically on a large scale. The high interfacial energy between the CNC-poly(tetrafluoroethylene) (PTFE) surface and torque induced by the shear force led to a large degree to the vertical alignment of CNC rods. An external DC electric field was added to further align the dipole moment of each CNC to the same direction. The as-obtained CNC film displayed excellent piezoelectric performance, and the piezoelectric coefficient was found to be 19.3 ± 2.9 pm/V, comparable to the piezoelectric coefficient d33 of poly(vinylidene difluoride) (PVDF) (20-30 pm/V). This work presents a new class of high-performance piezoelectric polymeric materials from renewable and biocompatible natural resources.

Unexpectedly high piezoelectric response in Sm-doped PZT ceramics beyond the morphotropic phase boundary region

Abstract Compositional design by multiphase coexistence is regarded as a guiding rule for material design to develop high-performance piezoelectric materials. An open question is whether a certain PZT composition outside of the morphotropic phase boundary (MPB) region can obtain high piezoelectric response like that close to MPB region. Here, a non-MPB composition, rhombohedral Pb(Zr0.54Ti0.46)O3 was selected as the parent material. The optimized electrical properties were obtained by Sm doping with a large piezoelectric coefficient d33 of 590 pC/N, a high planar electromechanical coupling factors kp of 57.1%, a large piezoelectric strain S of 0.31% (d33∗ = 632 pm/V), and a promising Curie temperature of 335 °C, compared to the commercial PZTs. The enhancement of piezoelectric response can be ascribed to the donor characteristics by Sm replacement, which contribute to polarization orientation of ferroelectric dipoles. This work broadens the domain of high-performance piezoelectrics by developing novel solid solutions beyond the MPB framework.

Atomic-scale origin of ultrahigh piezoelectricity in samarium-doped PMN-PT ceramics

Designing high-performance piezoelectric materials based on atomic-scale calculations is highly desired in recent years, following the understanding of the structure-property relationship of state-of-the-art piezoelectric materials. Previous mesoscale simulations showed that local structural heterogeneity plays an important role in the piezoelectric property of ferroelectrics; that is, larger structural heterogeneity leads to higher piezoelectricity. In this Rapid Communication, by combining first-principles calculations and experimental characterizations, we explored the atomic-scale origin of the high piezoelectricity for samarium-doped $\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-PT) ceramics, which possesses the highest piezoelectric ${d}_{33}$ of $\ensuremath{\sim}1500\phantom{\rule{0.16em}{0ex}}\mathrm{pC}\phantom{\rule{0.28em}{0ex}}{\mathrm{N}}^{\ensuremath{-}1}$ among all known piezoelectric ceramics. The impacts of various dopants on local structure and piezoelectric properties of PMN-PT ceramics were investigated in terms of the effective ionic radius and cation valence. Our results show that A-site dopants with a valence of 3+ are more effective to produce local structural heterogeneity in PMN-PT when compared with the A-site dopants with a valence of 2+, and a smaller dopant size leads to a larger variation of local structure. According to this study, the outstanding piezoelectricity in Sm-doped PMN-PT ceramics is attributed to the fact that $\mathrm{S}{\mathrm{m}}^{3+}$ is the smallest ions that can entirely go to the A site of PMN-PT rather than the B site. The present work may benefit the design of high-performance piezoelectric materials based on the concept of local structural engineering.

Enhanced mechanical energy harvesting capability in sodium bismuth titanate based lead-free piezoelectric

The demand for high-performance lead-free piezoelectric materials towards mechanical energy harvesting has been driven by the continuous requirements of self-powered applications such as wireless sensor network systems and biomedical devices, etc. Herein, manganese-doped sodium bismuth titanate based lead-free ternary piezoelectric system 0.92(Na0.5Bi0.5)TiO3-0.04(K0.5Bi0.5)TiO3-0.04BaTiO3 (NBT-KBT-BT) was developed and the critical role of manganese on tailoring the microstructure and electrical properties was investigated. The highest piezoelectric coefficient (d33) of 140 pC/N with figure of merit (d33 × g33) of 1790 × 10−15 m2/N has been achieved. Both high open-circuit voltage of ∼12.2 V and power density of ∼0.37 μW/mm3 were obtained based on cantilever-type energy harvester. This work provides a promising paradigm for the development of high-performance mechanical energy harvesting devices by tailoring the composition of lead-free piezoelectric ceramics.

Research on actuation performance of macro fiber composites based on third order shear deformation theory

Macro fiber composite (MFC) is a new type of high-performance smart piezoelectric material with an ultrathin section, which is used to decrease vibration and the noise of plate and shell structures due to high output and good flexibility. At present, the classical plate theory (CPT) has been adopted to study actuation performance of MFC. It does not consider shear deformation of an MFC integrated plate structure and cannot obtain the actuation force distribution of MFC, so that the accurate exerting position of the actuation force cannot be obtained. To solve this problem, this paper proposes that the third order shear deformation theory (TSDT) should be used to deduce the MFC actuation force formula which considers shear deformation of the MFC integrated plate structure and introduces a local displacement distribution function to ensure that the adhered interface between the MFC and the plate satisfy deformation compatibility and stress balance. Consider the end displacement calculation of an MFC integrated beam structure, for example. The comparison among the MFC actuation force formula based on TSDT, the MFC actuation force formula based on CPT, and the MFC integrated beam experiment indicates that the first can obtain higher calculation accuracy. On the basis of studying the MFC actuation force formula, the actuation simulation calculation of the plate by MFC is performed through making MFC equivalent to the actuation force and bending moment acting on plate structure to carry out the actuation experiment of an MFC integrated plate structure under the actuation of harmonic voltage of different amplitude values. The result shows that the experiment well matches the acceleration time history of simulation.

Ferroelectric mesocrystalline BaTiO3/Bi0.5K0.5TiO3 nanocomposites: Topochemical synthesis, enhanced piezoelectric and dielectric responses

Ferroelectric mesocrystalline nanocomposite is a promising nanomaterial for enlarged piezoelectric response and dielectric response obtained using lattice strain engineering. In this study, mesocrystalline BaTiO3/Bi0.5K0.5TiO3 (BT/BKT) nanocomposites were prepared via a two-step topochemical process. In the first step, a platelike layered titanate H1.07Ti1.73O4·nH2O (abbreviated as HTO) precursor was solvothermally treated in a Ba(OH)2 solution to synthesize a BaTiO3/HTO (abbreviated as BT/HTO) nanocomposite. In the second step, a BT/HTO-Bi2O3–K2CO3 mixture was heat-treated to obtain BT/BKT nanocomposite. The reactions occurring in the formation of BT/BKT nanocomposite are topochemical reactions. Nanostructural analysis shows that the BT/BKT nanocomposite is constructed from well-aligned [110]-oriented BT nanocrystals and [001]-oriented BKT nanocrystals. In the nanocomposite BT(001)/BKT(100), heteroepitaxial interface is formed, introducing a lattice strain at the interface owing to their lattice mismatch. The BT/BKT nanocomposite exhibits much larger d33* and εr values than those of individual BT and BKT mesocrystals. The enlarged piezoelectric and dielectric responses show the potential application of lattice strain engineering to mesocrystalline nanocomposites for high-performance lead-free piezoelectric materials.

High-Performance Sm-Doped Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3-Based Piezoceramics.

High-performance piezoelectric materials are pivotal to many electromechanical applications including piezoelectric actuators, sensors, and transducers. However, the general approach to achieve high piezoelectric properties by establishing morphotropic phase boundary (MPB) has limitation due to the weak anisotropy of the Gibbs free energy profile at the MPB region. Here, aliovalent Sm3+-doped 0.4Pb(Mg1/3Nb2/3)O3-(0.6-x)PbZrO3-xPbTiO3 piezoelectric ceramics were fabricated by a solid-state method, where the optimized piezoelectric coefficient d33 = 910 pC/N, dielectric constant εr = 4090, and Curie temperature TC = 184 °C were obtained at x = 0.352, being attributed to the synergistic contributions from the MPB and enhanced local structural heterogeneity. Rayleigh analysis was adopted to study the intrinsic and extrinsic contributions in Sm-doped PMN-PZ-PT ceramics, where the extrinsic contribution was found to be on the order of 25-67% at 4 kV/cm. Of particular significance is that a large signal d33* = 820 pm/V (at 20 kV/cm) with a minimal strain variation of 5% was achieved for a composition of x = 0.372 over the temperature range of 20-160 °C, being superior to those previously reported piezoelectric ceramic materials. This work offers a good paradigm to simultaneously achieve high piezoelectric properties with good temperature stability in ferroelectric ceramics, which have great potential for piezoelectric application at elevated temperatures.

Phase diagram determination of large piezoelectric response in BHT-BCT ceramics

High-performance lead-free piezoelectric materials are environmentally friendly and in great demand for electronic devices. In this study, the phase diagram and properties of Hf, Ca co-doped BaTiO3 (BHT-BCT) were investigated. A triple-point morphotropic phase boundary separating the rhombohedral, tetragonal and cubic phases for the (1-[Formula: see text])Ba(Ti0.85Hf0.15)O3-[Formula: see text](Ba0.7Ca0.3)TiO3 system exited at [Formula: see text] High piezoelectric properties with piezoelectric coefficients [Formula: see text] (572pC/N) and Curie temperature [Formula: see text] (90∘C) of 0.55Ba(Ti0.85Hf0.15)O3-0.45(Ba0.7Ca0.3)TiO3 are achieved in the BaTiO3-based ceramics.

Large electromechanical response in ferroelectrics: Beyond the morphotropic phase boundary paradigm

Ferroelectric based piezoceramics exhibiting large electromechanical response are used as sensors, actuators, and transducers in wide-ranging applications spanning sectors like space, defense, medical diagnostics, etc. In general, the large piezoelectric response in ferroelectric solid solutions is associated with a composition driven interferroelectric instability, commonly known as a morphotropic phase boundary (MPB). Here, we show that MPB is not necessarily required to achieve electromechanical response equivalent to, or even more than what can be achieved in MPB based ferroelectric solid solutions. We show this on two ferroelectric solid solution systems, namely, $(1--x)\mathrm{PbTi}{\mathrm{O}}_{3}\ensuremath{-}(x)\mathrm{Bi}(\mathrm{N}{\mathrm{i}}_{1/2}\mathrm{H}{\mathrm{f}}_{1/2}){\mathrm{O}}_{3}$ (PT-BNH) and $(\mathrm{Bi},\mathrm{La})\mathrm{Fe}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{PbTi}{\mathrm{O}}_{3}$ (BF-PT:La) which show large piezoelectric response (${d}_{33}\ensuremath{\sim}450\phantom{\rule{0.16em}{0ex}}\mathrm{pC}/\mathrm{N}$) and extraordinarily high electrostrain of \ensuremath{\sim}1.3%, respectively. Although analogous to the conventional MPB systems, the critical compositions of these two alloys mimic a two-phase structural state (cubic + tetragonal), detailed analysis that suggests that it is not so. The cubic phase is rather a manifestation of short correlation length of the tetragonal regions and appears when the system is compositionally driven from a normal ferroelectric state to a relaxor ferroelectric state. This proves that, in contrast to conventional MPB systems, the large electromechanical response of the critical compositions of PT-BNH and BF-PT:La is not due to interferroelectric instability enabled polarization rotation. In the absence of the MPB, the sole contributor to large electromechanical response is a process associated with domain wall motion, large local polarization, and (non-MPB) lattice softening. The generalized ideas derived from our investigation offer scope for expanding the basket of high-performance piezoelectric materials by exploring solid solutions outside of the MPB framework.

Bi(Zn0.5Ti0.5)O3 induced domain evolution and its effect on electrical property and thermal stability of 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics

0.8Na0.5Bi0.5TiO3-(0.2-x)K0.5Bi0.5TiO3-xBi(Zn0.5Ti0.5)O3 (NBT-KBT-BZT, x = 0–0.05 with interval of 0.01) lead-free piezoceramics were prepared and investigated. The addition of BZT has not led to deviation of rhombohedral-tetragonal morphotropic phase boundary, but apparently composition-dependent electrical property and monotonously improved thermal stability. The x = 0.02 has the optimal electrical property with remnant polarization, bipolar total strain, piezoelectric constant of 26.5 μC/cm2, 0.30%, 121 pC/N respectively, while the depolarization temperature is increased from 93 °C for x = 0–135 °C for x = 0.05 based on dielectric measurement. Detailed investigation reveals that the domain structure transforms from labyrinthian domain for x = 0 to coexistence of nanodomain and labyrinthian domain for x = 0.02, end up with large amount of nanodomain (x = 0.04). Such domain evolution should be responsible for the composition dependent electrical property and improved thermal stability. Our work confirms that domain engineering is an alternative method to develop high performance piezoelectric materials.

Multiple contributions to electrostrain in high performance PbTiO3−Bi(Ni1/2Hf1/2)O3 piezoceramics triggered by phase transformation

Piezoelectric materials, which mechanically respond to electrical stimulation and vice versa, typically exhibit high piezoelectricity at a morphotropic phase boundary (MPB). A thorough structural description is essential for understanding the origin of excellent piezoelectric properties. Herein, a comparative study of electric-field-driven structure and phase evolution has been conducted on MPB and non-MPB tetragonal composition in high performance system of PbTiO3–Bi(Ni1/2Hf1/2)O3 piezoceramics using in situ high-energy synchrotron X-ray diffraction. The results show that the MPB composition exhibits electric-field-driven reversible tetragonal-to-monoclinic transformation, whereas non-MPB composition does not. Direct evidence shows that the extensive phase transformation triggers multiple contributions to enhancing piezoelectric performance. Namely, it not only enables the unit cell parameters of coexisting phases easily change with an external electric field, but also enhances the domain switching and lattice strain. These results offer a unique perspective on MPB associated piezoelectricity enhancement, and will be helpful for developing high performance piezoelectric materials.

Concurrent anomalies in electric field-temperature dependence of direct/converse piezoelectric response in Bi0.5Na0.5TiO3-BaTiO3

Doping in bismuth sodium titanate (BNT)-based ceramic is often intended to realize excellent direct piezoelectric responses mainly through A-site substitution and generate ultrahigh strain behaviors mainly by B-site doping, which indicate the different effects of the doping on direct and converse piezoelectricity. Here, we reported simultaneous occurrences of anomalies in electric field and temperature dependence of direct/converse piezoelectric responses of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3(BNT-BT6) ceramics by detailed analyses of the weak-field piezoelectric coefficient d33, high-field piezoelectric coefficient d33∗, and small signal bias-field piezoelectric coefficient d33∗(E = 0). The multiple piezoelectric responses presented similar anomalies at critical field Ep = 20 kV/cm and critical temperature Tf = 120 °C. The analogous changes in direct/converse piezoelectric behaviors are highly related to the electric-field/temperature-driven phase transformation, which could boost polarization reorientation and domain switching to a lager extent. Particularly, the phase transition resulted in an obvious increase in high-field piezoelectric coefficient d33∗, and so offer a potential strategy for further development of high-performance lead-free piezoelectric materials.

Roll‐to‐Roll (R2R) Production of Ultrasensitive, Flexible, and Transparent Pressure Sensors Based on Vertically Aligned Lead Zirconate Titanate and Graphene Nanoplatelets

AbstractDespite extensive advances in the use of piezoelectric materials in flexible electronics, they have numerous shortcomings, including low efficiency, limited flexibility, and lack of transparency. Additionally, the production of these materials is often limited to small batch processes which are difficult to scale up for mass production. A novel method to produce ultrasensitive, high performance, flexible, and transparent piezoelectric materials where both lead zirconate titanate nanoparticles, and graphene nanoplatelets are aligned together in polydimethylsiloxane under an AC electric field in the thickness (“Z”) direction, is reported here for the first time. The electric field alignment improves the piezoelectric response along with transparency and also reduces the amount of filler required to achieve outstanding piezoelectric properties. The resulting ultrasensitive piezoelectric film is able to sense the pressure of a bird feather (1.4 mg) dropped from a certain distance, whereas at the touch of a fingertip, it can generate up to 8.2 V signal. Moreover, the mass production compatibility of the system is also demonstrated by producing a 3 m long and 15 cm wide large‐area sample via a novel 44′ long roll‐to‐roll manufacturing line which is designed and developed by the group.

High piezoelectric performance and domain configurations of (K0.45Na0.55)0.98Li0.02Nb0.76Ta0.18Sb0.06O3 lead-free ceramics prepared by two-step sintering

Research for high-performance lead-free piezoelectric materials has become an urgent issue from the environmental concern. Very limited attempts on two-step sintering had been made so far. In this study, (K0.45Na0.55)0.98Li0.02Nb0.76Ta0.18Sb0.06O3 ceramics were prepared by both conventional sintering and two-step sintering. Piezoelectric properties, microstructure and domain structure were found to change significantly with sintering methods and sintering conditions. Two-step sintering was performed in the way that temperature is first quickly raised to 1180 °C, kept for 1 min, then immediately cooled down to 1120 °C and maintained for a desired time length. The effects of dwelling time on piezoelectric performance and microstructure as well as domain structure were investigated. High piezoelectric properties of d33 = 455 pC/N, kp = 0.54 and k33 = 0.67 were obtained in a ceramic prepared under the dwelling time of 20 h. This ceramic also possesses a very good piezoelectric thermal-ageing stability over −50 °C–150 °C. Further investigation reveals that this ceramic has a quite uniform grain-size distribution with the average grain size of about 12 μm in microstructure and shows domain patterns of simple parallel stripes with a hierarchical nanodomain structure appearing inside some of broad stripes. The observed excellent piezoelectric performance is considered to associate closely with the unique domain structure.

Density functional theory computational study of ferroelectricity and piezoelectricity in BaTiO3/PbTiO3 (0 1 1) superlattices

The structure, ferroelectricity (FE), and piezoelectricity of epitaxial BaTiO3/PbTiO3 (BTO/PTO) (0 1 1) superlattices are studied using density functional theory calculations. Our results show that compressive strain arising from the SrTiO3 (0 1 1) substrate stabilizes the (BTO)m/(PTO)n (0 1 1) superlattices in orthorhombic phase with the FE polarization along [0 1 1] direction. Tuning the BTO contents significantly changes the structural, ferroelectric and piezoelectric properties. The FE polarization of superlattices significantly drops with increasing BTO contents, which can be attributed to depolarization of the PTO layers. The averaged c/a ratio of the whole superlattices exhibits anomalous non-monotonic relation with respect to BTO contents. Interestingly, our results predict the (0 1 1) superlattices can enhance the piezoelectric coefficient e33 with a maximum value at ~67% BTO concentration. This result suggests a potential avenue to design high performance piezoelectric materials with less Pb contents. In-depth analysis reveals the B-site Ti cation as the origin for the enhanced e33 value, which implies the potential of B-site cation engineering in perovskite heterostructure designs.

Ultrahigh Piezoelectric Properties in Textured (K,Na)NbO3 -Based Lead-Free Ceramics.

High-performance lead-free piezoelectric materials are in great demand for next-generation electronic devices to meet the requirement of environmentally sustainable society. Here, ultrahigh piezoelectric properties with piezoelectric coefficients (d33 ≈700 pC N-1 , d33 * ≈980 pm V-1 ) and planar electromechanical coupling factor (kp ≈76%) are achieved in highly textured (K,Na)NbO3 (KNN)-based ceramics. The excellent piezoelectric properties can be explained by the strong anisotropic feature, optimized engineered domain configuration in the textured ceramics, and facilitated polarization rotation induced by the intermediate phase. In addition, the nanodomain structures with decreased domain wall energy and increased domain wall mobility also contribute to the ultrahigh piezoelectric properties. This work not only demonstrates the tremendous potential of KNN-based ceramics to replace lead-based piezoelectrics but also provides a good strategy to design high-performance piezoelectrics by controlling appropriate phase and crystallographic orientation.

Significantly improved piezoelectric performance of PZT-PMnN ceramics prepared by spark plasma sintering.

A high-performance piezoelectric material, 0.95Pb(Zr0.52Ti0.48)O3-0.05Pb(Mn1/3Nb2/3)O3 (PZT-PMnN) ceramic, was prepared by using a spark plasma sintering (SPS) method. By systematically comparing the electrical properties, the spark-plasma-sintered sample was demonstrated to be superior to a conventionally sintered sample. With respect to conventionally sintered ceramic, the d33 of spark-plasma-sintered ceramic increases from 323 pC/N to 412 pC/N, and the increases from 318 pm V−1 to 553 pm V−1. More importantly, the mechanical quality factor (Qm) reaches 583, which is three times higher than the conventionally sintered sample (Qm ∼ 182). Furthermore, the SPS method was found to be capable of promoting other electrical properties simultaneously. Therefore, the SPS method is proposed to be an effective processing method to fabricate PZT-PMnN ceramics of higher performance.

Critical Role of Monoclinic Polarization Rotation in High-Performance Perovskite Piezoelectric Materials.

High-performance piezoelectric materials constantly attract interest for both technological applications and fundamental research. The understanding of the origin of the high-performance piezoelectric property remains a challenge mainly due to the lack of direct experimental evidence. We perform insitu high-energy x-ray diffraction combined with 2D geometry scattering technology to reveal the underlying mechanism for the perovskite-type lead-based high-performance piezoelectric materials. The direct structural evidence reveals that the electric-field-driven continuous polarization rotation within the monoclinic plane plays a critical role to achieve the giant piezoelectric response. An intrinsic relationship between the crystal structure and piezoelectric performance in perovskite ferroelectrics has been established: A strong tendency of electric-field-driven polarization rotation generates peak piezoelectric performance and vice versa. Furthermore, the monoclinic M_{A} structure is the key feature to superior piezoelectric properties as compared to other structures such as monoclinic M_{B}, rhombohedral, and tetragonal. A high piezoelectric response originates from intrinsic lattice strain, but little from extrinsic domain switching. The present results will facilitate designing high-performance perovskite piezoelectric materials by enhancing the intrinsic lattice contribution with easy and continuous polarization rotation.

High-Throughput Investigation of a Lead-Free AlN-Based Piezoelectric Material, (Mg,Hf)xAl1-xN.

We conducted a high-throughput investigation of the fundamental properties of (Mg,Hf)xAl1-xN thin films (0 < x < 0.24) aiming for developing high-performance AlN-based piezoelectric materials. For the high-throughput investigation, we prepared composition-gradient (Mg,Hf)xAl1-xN films grown on a Si(100) substrate at 600 °C by cosputtering AlN and MgHf targets. To measure the properties of the various compositions at different positions within a single sample, we used characterization techniques with spatial resolution. X-ray diffraction (XRD) with a beam spot diameter of 1.0 mm verified that Mg and Hf had substituted into the Al sites and caused an elongation of the c-axis of AlN from 5.00 Å for x = 0 to 5.11 Å for x = 0.24. In addition, the uniaxial crystal orientation and high crystallinity required for piezoelectric materials to be used as application devices were confirmed. The piezoelectric response microscope indicated that this c-axis elongation increased the piezoelectric coefficient almost linearly from 1.48 pm/V for x = 0 to 5.19 pm/V for x = 0.24. The dielectric constants of (Mg,Hf)xAl1-xN were investigated using parallel plate capacitor structures with ∼0.07 mm2 electrodes and showed a slight increase by substitution. These results verified that (Mg,Hf)xAl1-xN is a promising material for piezoelectric-based application devices, especially for vibrational energy harvesters.