Effects of lattice parameters on piezoelectric constants in wurtzite materials: A theoretical study using first-principles and statistical-learning methods

Abstract

Longitudinal piezoelectric constant (e 33 ) values of wurtzite materials, which are listed in a structure database, are calculated and analyzed by using first-principles and statistical learning methods. It is theoretically shown that wurtzite materials with high e 33 generally have small lattice constant ratios (c/a) almost independent of constituent elements, and approximately expressed as e 33 / c/a % (c/a) 0 with ideal lattice constant ratio (c/a) 0 . This relation also holds for highly-piezoelectric ternary materials such as Sc x Al 1%x N. We conducted a search for high-piezoelectric wurtzite materials by identifying materials with smaller c/a values. It is proposed that the piezoelectricity of ZnO can be significantly enhanced by substitutions of Zn with Ca. © 2018 The Japan Society of Applied Physics I n recent times, owing to their suitable mechanical and semiconducting properties, piezoelectric wurtzite semiconductors such as ZnO and GaN have received a lot of attention in the form of piezotronics and piezo-phototronics device materials.1) The wurtzite-type piezoelectric materials, especially AlN, have another advantage that these can be used in high-temperature environments, e.g., as sensors in automobile engines, because their noncentrosymmetric structures are stable even at high temperatures.2,3) However, the piezoelectric constants of wurtzite-type materials are generally much smaller than those of the perovskite-based materials such as Pb(Zr x Ti 1−x )O 3 , known as PZT, by few orders. It remains a challenge to explore better piezoelectric wurtzite materials; there are many reports aiming to enhance piezoelectricity by element doping or codoping into parent materials. 4-7)Among the wurtzite materials, the highest piezoelectricity has been experimentally discovered for Sc x Al 1−x N (about 25 pC=N for x ∼ 0.5).2,3) First-principles calculations have shown the microscopic effects of Sc on the piezoelectricity in Sc x Al 1−x N by demonstrating an enhancement in piezoelectricity with increase in x. 8,9) Tasnádi et al. have revealed that the piezoelectric enhancement comes from the large responses of atomic positions to external strain and the significant softening of elastic constant. 8) However, novel materials which are superior to Sc x Al 1−x N have not been synthesized yet as there are no clear and general material-design criteria practically usable for enhancing the piezoelectricity of wurtzite materials. It has been proposed theoretically that there exists a relationship between piezoelectricity and microscopic structures, 10) but the physical mechanism behind the relation with intricate parameters is not fully understood yet. Therefore, better understanding of piezoelectricity in wurtzite materials might lead to simple design criteria making it possible to find a controllable key parameter describing wurtzite piezoelectricity with the help of first-principles and machine learning techniques which have generated a great interest in the recent times. 11,12) In this study, we calculate longitudinal...

Large Piezoelectric Response and Ferroelectricity in Li and V/Nb/Ta Co-Doped w-AlN

“…Usually wurtzite crystals with smaller c/a ratio show higher piezoelectric response [32]. Our calculated c/a ratio of…”

“…First, we examine how the doping changes the ratio of the lattice parameters a and c (i.e., c/a ratio) in w-AlN, which plays an important role in the origin of electric polarization as well as the piezoelectric response of wurtzites [32,33].…”

Significant Enhancement of Piezoelectric Response in AlN by Yb Addition

“…Furthermore, the lattice parameter ratio ( c/a ) of the wurtzite structure decreases as the quantity of additional elements increases [ 1 , 2 , 9 , 16 ]. Changes in the piezoelectric stress constant, e 33 , are generally corelated with changes in the lattice parameter [ 17 ].…”

Ferroelectricity and Large Piezoelectric Response of AlN/ScN Superlattice

“…. High performance RF lters made of AlN based resonators also show great promise for mobile communication systems 1,68 . However, the low electromechanical coupling coecient, which is closely related to the piezoelectric coecients, is the main disadvantage of pure w-AlN.…”

“…Interestingly, we can also explain this increase of e 33 in terms of the c/a ratio. Recently a linear relation between e 33 and the c/a ratio has been proposed for various known wurtzite materials 68 . In Fig.…”