Atomic-scale origin of piezoelectricity in wurtzite ZnO

Abstract

ZnO has been extensively studied by virtue of its remarkably high piezoelectric responses, especially in nanowire forms. Currently, the high piezoelectricity of wurtzite ZnO is understood in terms of the covalent-bonding interaction between Zn 3d and O 2p orbitals. However, the Zn 3d orbitals are not capable of forming hybridized orbitals with the O 2p z orbitals since the Zn ion is characterized by fully filled non-interacting 3d orbitals. To resolve this puzzling problem, we have investigated the atomicscale origin of piezoelectricity by exploiting density-functional theory calculations. On the basis of the computed orbital-resolved density of states and the band structure over the G-M first Brillouin zone, we propose an intriguing bonding mechanism that accounts for the observed high piezoelectricityintra-atomic 3d z 2-4p z orbital self-mixing of Zn, followed by asymmetric hybridization between the Zn 3d z 2-4p z self-mixed orbital and the O 2p z orbital along the polar c-axis of the wurtzite ZnO.

β-CuGaO2 as a Strong Candidate Material for Efficient Ferroelectric Photovoltaics

“…The most prominent feature in the computed DOSs is a remarkable enhancement of the 3d z 2 - and 4p z -orbital DOSs of Ga (for the energy range between −0.5 and 0 eV below the valence-band top) upon the transition to the ferroelectric Pna 2 1 state, indicating the intra-atomic Ga 3d z 2 –4p z orbital self-mixing and the consequent formation of an asymmetric-shaped mixed orbital (ϕ m ), as depicted in Figure c. This mechanism of the intra-atomic orbital self-mixing was proposed for a number of oxides such as BFO, InMnO 3 , and semiconducting ZnO. − Subsequently, these asymmetric mixed orbitals at Ga (ϕ m ) interact with the two neighboring apical O 2p z orbitals [Figure d]. Because of the antisymmetric nature of the 2p z orbital wave function along the z -direction, the Ga ϕ m –O 2p z orbital overlapping is parity-allowed only for one neighboring Ga–O bond.…”

One-Step Synthesized ZnO np-Based Optical Sensors for Detection of Aldicarb via a Photoinduced Electron Transfer Route

“…ZnO crystals of various shapes in the hexagonal wurtzite crystalline phase were synthesized by different synthesis methods with n-type semiconducting nature. ZnO in the doped and undoped form has been used for several applications such as in gas, chemical, and heavy metal ion sensors. − ZnO compounds formed with considerable covalent bonding between Zn 3d and O 2p orbitals lead to wide-band-gap materials . ZnO of various shapes exhibits two luminescence bands: one is located at the absorption edge, also called the edge luminescence peak, that occurs at a shorter wavelength and the other is a wide band at higher wavelengths, generally located in the green wavelength range. , The edge luminescence is excitonic, and the green luminescence may be obtained for various reasons such as impurities, Zn and O vacancies, and interstitial ions, but the principal reason behind this is yet to understand. , However, the luminescence properties can be used for optical sensors and biosensors for the detection of desired analytes.…”

Ultra-Stable and Durable Piezoelectric Nanogenerator with All-Weather Service Capability Based on N Doped 4H-SiC Nanohole Arrays

“…The distortion of the tetrahedron along c-axis leads to the separation of the cation and anion centers of 4H-SiC, forming c-axis-oriented dipole moments. Once an external force is applied along the c-axis, the deformation of the tetrahedral units of 4H-SiC will significantly strengthen the dipole moments and enhance piezoelectricity [ 31 , 37 – 39 ]. Furthermore, N doping will enhance the piezoelectricity of 4H-SiC by adjusting crystal structure and inducing dipoles.…”