Stuctural Phase Transition and Electronic Properties of AISb Nanocrystal Neha Tyagi , Anurag Srivastava Advance Material Research Laboratory ABV- Indian Institute of Information Technology and Management Gwalior (M.P), India nehatyagi.phd@gmail.com, profanurag@gmail.com Abstract- Density functional theory (DFT) based ab-initio approach has been used to investigate the structural stability of -lnm sized AlSb nanocrystal in its zinc blende (B3), rocksalt (Bl) and CsCl (B2) type phases under high compression. The self consistent total energy calculations have been performed for analyzing the stability of the material and found that B3 type phase is most stable amongst the other considered phases. It is revealed that under compression, the original B3 type phase of AlSb nanocrystal transforms to Bl type phase at a pressure of about 8.9 GPa, which is larger than that of bulk crystal. The ground state properties such as lattice parameter, bulk modulus and pressure derivative have been calculated for all the three stable phases of AlSb nanocrystal. The electronic band structure analysis inds that the band gap of AlSb nanocrystal in its most stable (B3) phase is comparatively lower than its bulk counterpart. Keywords-phase transition; nanocystal; AISb; irst -principle I. [NTRODUCTION Semiconductor nanocrystals of III-V compounds are of great signiicance due to their applications in various electronic and optical devices [1]. Rapid advances that have occrred in the preparation and characterization of nanocrystals, inally enables the studies of ransfomations between stable states of fmite systems. Aluminum antimony (A1Sb) seems to be a promising candidate for transistors and p-n junction diodes due to large band gap [2]. A1Sb nanoclusters have also been synthesized by nanoscale electrodeposition [3,4]. Experimentally, the size dependent solid-solid ransition have been irstly reported by Tolbert and Alivisatos[S] in 1994, where they observed a wurtzite to rocksalt phase ransition in CdSe nanocrystal. A pressure induced irst-order sructural phase transition rom wurtzite to rocksalt type sructure has been observed in GaN nanocrystals at around 48.8 GPa using x-ray difraction technique [6]. Similarly Lei et al.[7] have investigated the wurtzite to rocksalt phase ransfonnation in AIN nanocrystal with an average size of lOmn and 4Smn at around 14.SGPa and 21.SGPa respectively. Zhang et al. [8] used the pseudopotential total-energy approach to analyzed the stability of two high pressure structures, the AS (�-Sn) and rocksalt structures, for zinc blende III-V semiconductors andfound that the bulk AISb shows zinc blende to rocksalt transformation at S.6GPa. Viswanatha et al. [9] have investigated the elecronic sructure of group III-V and II-VI semiconducting nanocrystals using ull potential linearized augmented plane wave (FP-LAPW) method and tight-binding 978-1-4673-0074-2/11/$26.00 @2011IEEE model. Recently our group has also performed the irst principle calculation to investigate the effect of shape on the structural and elecronic properties of Pb and Si nanowires [[0,1[]. The review of literature shows that probably no experimental as well as theoretical research has been performed on the pressure induced phase ransition in A1Sb nanocrystal. Inspiring this and the technological importance of the material, we thought it pertinent to perform the present analysis. II. COMPUTATIONAL DETAILS Ab-initio pseudopotential approach as implemented in the Atomistix Toolkit Virtual Nano Lab (ATK-VNL) [[2] has been used for the present study. The computation has been made in self consistent manner using steepest descent geometric optimization technique with Pulay algorithm for iteration mixing. A mesh cut-off of [00 Rydberg has been used throughout the study. The Brilloun-zone (BZ) integration is performed with a Monkhorst-Pack scheme using lxlxSO k points. The cutoff energy and the number of k points re varied to test the convergence and are found to converge within the force tolerance of O.OSeV/A for the reported value. The exchange corelation unctional described within the local density approximation (LDA-PZ) proposed by Perdew and Zunger [13] and with generalized radient approximation revised-PBE (rev-PBE) as proposed by Zhang and Yang [14,15], are used for the computation of total energies of A1Sb nanocrystal in its zinc blende (B3), rocksalt (B[) and CsCI (B2) type phases. The total energy for B3 type phase of A1Sb nanocrystal with GGA rev-PBE potential is -299.07eV and with LDA-PZ potential is -293.24eV, which indicates that GGA rev-PBE potential is quite good for the computation of total energy. The nanocrystals have been assumed to be roughly spherical and their diameter can be calculated by using the relationship of lattice parameter and number of atoms present in the nanocrystal, given elsewhere [9]. Bulk modulus and pressure derivaties have been analyzed using Munaghan's equation of state[16]. III. RESULTS ND DISCUSSIONS A. Stabiliy analysis andphase ransition The stability of A1Sb nanocrystal of -1 mn size has been analyzed in zinc blende (B3), rocksalt (B[) and CsCI (B2) ype phases using density unctional theory (DFT) approach. The computated lattice parameter (6.235 A) for bulk AISb in B3 421