Contents lists available at ScienceDirect Physica B journal homepage: www.elsevier.com/locate/physb Effect of pressure and doping on lattice structure of zinc oxide Mahmoud Zolfaghari Physics Department, University of Sistan and Baluchestan, Zahedan 9816745785, Iran ARTICLE INFO Keywords: Semiconductor XRD Nanoparticle Pressure ABSTRACT The semiconductor ZnO belongs to the IIb-VI binary compound. It has a high exciton binding energy of 60 meV. The bonding in these materials is covalent with some ionic character. Induced changes on the physical properties of Mn doped ZnO samples due to different dopant concentrations and pressure were evaluated. The results obtained showed higher solubility limit for Mn doped ZnO due to pressure. The trend of XRD results for higher Mn concentration (9 at%) as pressure increases, was towards doping improvement. The XRD, SEM and UV–vis study of the samples also revealed that there were variations in the lattice parameters, nanoparticle size and bandgap energy of the doped and pressurized doped samples. Further, the directions of variation of bandgap energy values and calculated particle size, as well as SEM values of the doped samples due to pressure variation were found to be the same i.e. all of them together either increase or decrease as pressure varies. However, these variations were found to be opposite to that of lattice constants (all a and most c values) variation for both Mn dopant concentrations (3 at% and 9 at%). These physical variations of unpressurized doped samples can be attributed to the change in the polar bonding of the elemental constitutions in the lattice. While for the pressurized doped samples, the variations attributed to repulsion of lone pairs as well as change in the electronegativity of the system. 1. Introduction The semiconductor ZnO belongs to the group IIb-VI and has gained numerous interests [1–5]. Due to the substantial ionic character that exists in these materials, the bandgap increases beyond that expected from the covalent bonding. The ionic character of ZnO resides at the borderline between the covalent and ionic semiconductors. In recent years, mixed transition-metal oxides with spinel structure have attracted much attention. Mn doped ZnO predicted to be a room- temperature diluted magnetic semiconductor [6]. Therefore, the Mn- Zn-O ternary systems belong to a class of interesting and useful materials in terms of their electrical and magnetic properties [7,8]. As one of the important mixed transition-metal oxides with spinel structure, ZnMn 2 O 4 is a promising functional material and has become the focus of various researches owing to its potential applications [9– 11]. The full-potential augmented plane wave plus local orbitals method is used to study the trends for structural, electronic and optical properties of the ZnB 2 O 4 spinel oxides depending on the type of B element (B are Al, Ga and In). The calculated results show as pressure increases band gap (direct and indirect) increases almost linearly [12]. The role of d states in defining the electronic properties of the II-VI semiconductors has been discussed [13]. It has been reported that the p-d hybridization at Γ repels the valence without affecting the conduc- tion band minimum. The three crystal structures shared by ZnO are wurtzite, zinc blende, and rock salt (or Rochelle salt). The wurtzite structure of ZnO is the thermodynamically stable phase under ambient conditions; hence it is the most common. It consists of two interpenetrating hexagonal close-pack sublattices, each of which contains either Zn or O, they lie along the c-axis and are displaced by the amount of internal parameter u=3/8 in fractional coordinates [3]. The zinc–oxygen distance along the c-axis (d Zn–O =0.190 nm) is slightly shorter than that of other Zn–O bonds (d Zn–O =0.198 nm). The (0001)-Zn surface has been found to be chemically active, while the (0001)-O terminated surface is chemically inert [14,15]. These are the most common polar surfaces as they produce positively charged ions Zn-(0001) and negatively charged ions O- (0001) surfaces, resulting in a normal dipole moment and spontaneous polarization along the c-axis, as well as a divergence in surface energy. To maintain a stable structure, the polar surfaces generally have facets or exhibit massive surface reconstruc- tions, but ZnO – ± (0001) are exceptions: they are atomically flat, stable and without reconstruction [16,17].Efforts to understand the superior stability of the ZnO ± (0001) polar surfaces are at the forefront of recent research on surface physics [14,18–20]. The other two most commonly observed facets for ZnO are {2110} and {0110}, which are non-polar surfaces and have lower energy than the {0001} facets. http://dx.doi.org/10.1016/j.physb.2016.10.029 Received 11 August 2016; Received in revised form 20 October 2016; Accepted 21 October 2016 E-mail address: mzolfaghari@phys.usb.ac.ir. Physica B 505 (2017) 45–51 0921-4526/ © 2016 Elsevier B.V. All rights reserved. Available online 22 October 2016 crossmark