Materials Science in Semiconductor Processing 122 (2021) 105467 Available online 1 October 2020 1369-8001/© 2020 Elsevier Ltd. All rights reserved. Full length article Structural, electronic, optical and thermoelectric properties in the phases of AgTaO 3 Salman Ali Khan a , Hidayat Ullah Khan b , Shahid Mehmood a , Zahid Ali a, * a Department of Physics, Center for Computational Materials Science, University of Malakand, Chakdara, Dir (Lower), 18800, Pakistan b Department of Physics, University of Peshawar, Peshawar, 25120, Pakistan A R T I C L E INFO Keywords: Perovskite oxide Structural stability Electronic band profles Optical properties Thermoelectric properties ABSTRACT Structural phases of silver tantalate (AgTaO 3 ) such as rhombohedral (R3c), monoclinic (P2/m), orthorhombic (Cmcm), tetragonal (P4/mbm) and cubic (Pm-3m) have been investigated using density functional theory (DFT) to verify the previous work. Structural parameters of all these phases are in agreement with the experimental re- sults. Formation enthalpies and cohesive energies of these phases reveal that the monoclinic phase is more stable than the rhombohedral phase. On the basis of electronic properties; direct and indirect band gap transitions are identifed as follows, R3c, P2/m and Pm-3m have indirect band gaps (3.086 eV, 2.970 eV and 2.921 eV) whereas Cmcm and P4/mbm have direct band gaps (2.180 eV, 2.762 eV). In view of optical properties AgTaO 3 , in all phases, is found promising for optoelectronic devices in the visible region. The present compound showed a high dielectric constant in orthorhombic phase. Thermoelectric properties such as Seebeck coeffcient 2955 μV/K, electrical conductivity 3.84 × 10 20 1/Ωm.s and power factor 1.17 × 10 12 W/K 2 ms showed that AgTaO 3 is a potential candidate for thermoelectric devices because of low electrical conductivity and high power factor. 1. Introduction Perovskites have attracted the attention of material scientists because of their cost-effectiveness, effciency, easy processing and more versatile properties. Until present, researchers are working on perov- skites in the feld of solar cells because of their low cost and great eff- ciency [1–7]. Perovskites are also used as photo-catalytic for the production of hydrogen to store energy [8,9]. Beside solar cells, they are effective for light emission, electroluminescent diodes, optically pum- ped lasers [10] and X-ray photon detectors [11]. They can be utilized as a microwave dielectric in wireless communications [12], uses in piezoelectricity [13], piezoelectric sensors, actuators, ultrasound gen- eration and in magneto electrics [14]. AgTaO 3 belongs to the perovskite family and was synthesized by Francombe and Lewis [15] at 1473 K by squeezing mixtures of Ag 2 O and Ta 2 O 5 . It was reported that the compound exhibits a series of phase transitions at various temperatures. At T ≤ 663 K, it exists in the rhombohedral phase which transforms into the orthorhombic phase with monoclinic distortion in the temperature range of 667–693 K. At T = 703–773 K, the compound is reported in the tetragonal phase and fnally adopts cubic phase at T ≥ 779 K [15–22]. Mahmood et al. [23] studied electronic structure, thermoelectric and optical properties by using density functional theory (DFT) and reported that cubic AgTaO 3 is 1.64 eV band gap semiconductor. Hongyu et al. [24] reported that AgTaO 3 is an excellent high-temperature solid lubricant and chemically inert compound. Soon et al. [21] reported that the compound is para- electric at room temperature with space group R 3c. Contrary to its room temperature paraelectric nature, one report says that AgTaO 3 is ferroelectric below 130 K temperature [27]. Erdinc and Dede [25] studied cubic AgTaO 3 in paraelectric phase under different pressures and reported that the band gap and dielectric constant in- crease as a function of increase in pressure. While studying the photo- catalytic activity, Jaim et al. [8] reported that AgTaO 3 is potentially effective for hydrogen production. Kato et al. [26] studied the role of Ag + in the structure and photocatalytic properties in AgMO 3 (M: Ta and Nb) and reported that AgTaO 3 is phoyocatalitically active for pure water splitting in ultraviolet region of electromagnetic spectrum. Xu et al. [27] enhanced the photocatalytic activity and light sensitivity of AgTaO 3 by decorating Ag nanoparticles in the presence of visible light. Yet far, the structural stability of the compound AgTaO 3 has not been fully determined experimentally. Francombe and Lewis [15] reported the orthorhombic phase at room temperature and tetragonal phase at * Corresponding author. Department of Physics, University of Malakand, Chakdara, Pakistan. E-mail address: zahidf82@gmail.com (Z. Ali). Contents lists available at ScienceDirect Materials Science in Semiconductor Processing journal homepage: http://www.elsevier.com/locate/mssp https://doi.org/10.1016/j.mssp.2020.105467 Received 19 April 2020; Received in revised form 28 July 2020; Accepted 22 September 2020