Giant Piezoelectric Response in Superionic Polar Semiconductor

Abstract

by lead zirconate titanate [Pb(Zr,Ti)O 3 or PZT],are the most widely used materials for applications. [5][6][7] From the viewpoint of the sustainable development of the world, many efforts have been devoted to the development of lead-free piezoelectric materials, [5][6][7] but its achievement is still challenging. Scientific research activities seem to be culminated, and a new guideline to a future research direction is required. [1] In this work, we newly propose a relatively conductive polar semiconductor as a potential piezoelectric material, although it has been believed that conduction electrons disfavor the formation of electric polarization. [8] AgCrSe 2 has a polar crystal structure of the R3m space group at room temperature, which allows piezoelectric effects. AgCrSe 2 crystallizes in a hexagonal structure with Ag layers and CrSe 6 octahedral layers stacking alternatively along the c axis, [9] as shown in Figure 1a. In between CrSe 6 layers, Ag + ions lie in one of the equivalent interstitial sites (α-sites and β-sites in Figure 1a), which are energetically degenerated. [9] It has been reported that the occupation of Ag + ions undergoes an order-to-disorder transition at 450-475 K (T OD ). In the disordered state above T OD , Ag + ions are distributed randomly in α and β sites with equal probability, whereas below T OD , only one of the interstitial sites is fully occupied, lowering the crystal symmetry from R-3m to R3m. Ag + ions are mobile in 2D space sandwiched by CrSe 6 layers, and the inplane ionic conductivity is high (≈ 3 × 10 −4 S cm −1[10] ) even at room temperature. Reflecting the disorder effect of Ag + ions, ultralow thermal conductivity due to strong phonon scatterings has been reported. [9,11,12] The thermoelectric Figure of merit of Ag 1-δ CrSe 2 is as large as ≈0.5 at 723 K, [12] which ensures that AgCrSe 2 is a promising thermoelectric material. [13] In this study, we report an excellent piezoelectric performance of AgCrSe 2 , by measuring the inverse piezoelectric effect, i.e., the generation of a strain upon application of an electric field, along the perpendicular direction to the conduction layers of AgCrSe 2 crystals. The carrier density of AgCrSe 2 was successfully controlled by subtle nonstoichiometry (presumably the Ag deficiency) dependent on the crystal growth conditions, which enables the study of the resistivity dependence of piezoelectric effect in this system. Though our AgCrSe 2 single crystals are not perfect insulators, we still observe large displacements of the crystals in response to A lead-free piezoelectric material whose performance is comparable to that of market-dominant lead-based ones has been strongly desired for the development of environmentally friendly piezoelectric devices. In spite of intensive research activities, however, few effective alternatives have been found due to severe requirements such as the absence of conducting carriers screening the electric polarization. Here, a polar semiconductor, AgCrSe 2 , is demonstrated as a promising piezoelectri...

Enhanced magnetopiezoelectric effect at the Néel temperature in CaMn2Bi2

“…For the MPE measurement, we used a laser Doppler vibrometer equipped with a liquidnitrogen optistat for low-temperature measurements [21]. The laser Doppler vibrometry allows for non-contact detection of subpicometer-level tiny vibrations [32][33][34][35] by measuring the Doppler frequency shift of the scattered light from the sample using a two-beam laser interferometer. This technique has been widely used in room-temperature experiments for the characterization of piezoelectric thin films [34,35] and for the detection of small cantilever oscillations with resonant frequencies [36].…”

“…1 to applied electric currents were detected using the Doppler effect of red laser (wavelength of 633 nm) irradiated through a quartz window of the optistat. By combining the laser Doppler vibrometer with a fast Fourier transform (FFT) analyzer [32][33][34][35], we obtained a frequency spectrum of the vibration velocity of the sample. The obtained velocity was then numerically integrated with respect to time using the FFT analyzer, and finally the frequency dependence of the vibration amplitude of the sample was obtained.…”

Group-theoretical classification of multipole order: Emergent responses and candidate materials

“…The MPE effect may be applicable in the field of the antiferromagnetic spintronics [106][107][108]. Furthermore, the MPE materials may be useful for metal piezoelectric devices [109,110]. Finally, we discuss a dichromatic transport of electrons.…”

Observation of a Magnetopiezoelectric Effect in the Antiferromagnetic Metal EuMnBi2

“…The search for piezoelecric materials thereby has been carried out with insulators and semiconductors. Nevertheless, the realization of highly-conductive piezoelectric materials could offer new applications of piezoelectricity because of their compatibility with electrical circuits [8].…”