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April 16, 2026

DFT Study of Ca2NaXO6 (X = Cl or Br) Double Perovskites: Structural, Electronic, Mechanical, Thermoelectric, and Optical Properties

Key Points

The research aims to analyze the structural, electronic, mechanical, thermoelectric, and optical properties of Ca2NaXO6 double perovskites.
First-principles calculations using FP-LAPW and WIEN2k
Geometry optimization for structural analysis
Calculation of elastic constants for mechanical stability
Band structure analysis for electronic properties
Boltzmann transport theory for thermoelectric performance
Cubic Fm3m structure confirmed for both compounds with specific lattice parameters
High mechanical stability with significant hardness and brittleness indicated
Direct band gaps of 1.75 eV for Cl and 2.21 eV for Br, with specific UV absorption edges
Thermoelectric performance shows a power factor and ZT of approximately 0.74 at 1000 K
Identified as suitable for UV filtering and high-temperature waste heat harvesting

Abstract

First-principles calculations (FP-LAPW, WIEN2k) were used to investigate the double perovskites Ca2NaXO6 (X = Cl, Br). Geometry optimization yields the cubic Fm 3m structure (no. 225) with a = 7. 4693 Å (Cl) and a = 7. 6236 Å (Br), indicating thermodynamic stability. Elastic constants satisfy the Born’s mechanical stability criteria, with high resistance to compression and shear; indicators (Pugh’s and Poisson’s ratios, Cauchy’s pressure) point to high hardness and intrinsic brittleness. Zener/percentage anisotropy show mild elastic anisotropy for Ca2NaClO6 (bulk modulus essentially isotropic) and near‑isotropy for Ca2NaBrO6. KTB‑mBJ band structures reveal direct Γ–Γ gaps of 1. 75 eV (Cl) and 2. 21 eV (Br), corresponding to absorption edges at 709 and 561 nm, respectively. Optical spectra exhibit strong ultraviolet absorption consistent with O‑2p → (Ca‑d, X‑p) transitions. Boltzmann transport (constant relaxation time, τ = 1 × 10‒14 s) combined with a Slack‑model lattice term gives temperature‑rising power factor and ZT ≈ 0. 74 at 1000 K for both halides, benchmark‑consistent with published Sr‑halide and iodide analogues. Together, the direct visible‑edge gaps, UV selectivity, and stable high‑T thermoelectric performance identify Ca2NaClO6 and Ca2NaBrO6 as multifunctional energy materials spanning UV‑optoelectronic filtering/detection and high‑temperature waste‑heat harvesting.

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