Physics Letters A 372 (2008) 1910–1914 www.elsevier.com/locate/pla Ab initio investigation of phase separation in Ca 1-x Zn x O alloys R. Miloua *,1 , Z. Kebbab, F. Miloua, N. Benramdane Laboratoire d’Elaboration et de Caractérisation des Matériaux, Faculté des Sciences de l’Ingénieur, BP 89, Université Djillali LIABES, Sidi-Bel-Abbès, Algeria Received 4 August 2007; received in revised form 6 October 2007; accepted 18 October 2007 Available online 4 November 2007 Communicated by R. Wu Abstract First-principles study of the ground-state properties and the stability of Ca 1-x Zn x O solid solutions is presented using the full-potential lin- earized augmented plane wave (FP-LAPW) method. We employed the local density approximation (LDA) to the exchange-correlation potential. It is found that the structural parameters, i.e., lattice constants and bulk moduli deviate from the linear function of the composition x . We determined the equation of state of the alloys and showed an increasing compressibility function of composition. The formation energy is viewed as an ener- getic balance between pure structural constraints and quantum chemical effects. Thus, a phase separation over the whole range of concentration is expected. The origin of the miscibility gap has a chemical nature. Also, the thermodynamic stability of the alloys was investigated.  2007 Elsevier B.V. All rights reserved. Keywords: Phase separation; CaZnO; FP-LAPW; DFT-LDA 1. Introduction Mixed crystals based on wide band gap ZnO compound have been of great interest in the last few years because of the rele- vance of their electronic, optical and catalytic properties. These materials find many applications such as short wavelength light- emitters, solar cells, catalysts, etc. Recently, the MgZnO alloy has been in focus both in experiments [1–3] and theory [4,5] due to the possibility of increasing the band gap energy of ZnO. In contrast, CaZnO has received less attention both in the exper- imental and in the theoretical side. This motivates us to report a structural and thermodynamic study on possibility to form the Ca 1-x Zn x O alloy. CaZnO is a promising mixed oxide, it has been used as a catalyst for N 2 O decomposition [6], CH 4 selec- tive conversion [7] and in many other applications. In the present work, we employed the Full-Potential Lin- earized Augmented Plane Wave (FP-LAPW) method [8] to study the ground-state properties and the formation energy of * Corresponding author. Tel.: +213 50 71 61 56. E-mail address: mr_lecm@yahoo.fr (R. Miloua). 1 Laboratoire d’Elaboration et de Caractérisation des Matériaux. Faculté des Sciences de l’Ingénieur, Université Djillali Liabès, Sidi-Bel-Abbès 22000, Al- geria. the alloys. Thus, the disordering effect on the formation energy is introduced using a cluster expansion approach. The predicted trends are explained on the basis of a structural-chemical en- ergetic balance. Further, the thermodynamic phase diagram is established and the critical temperature is estimated. The rest of the Letter is organized as follows. In Section 2, we briefly describe the calculation procedure. Results and dis- cussions are presented in Section 3 and the Letter is concluded in Section 4. 2. Method of calculation Our calculations have been made using FP-LAPW approach within the framework of the Density Functional Theory (DFT) [9,10] as implemented in WIEN2k [11] code. The exchange- correlation contribution to the total energy is described within the Local Density Approximation (LDA) [12]. Kohn–Sham wave functions were expanded in terms of spherical harmonic functions inside the non-overlapping muffin-tin spheres sur- rounding the atomic sites (MT spheres) and in Fourier series in the interstitial regions. Inside the MT spheres of radius R MT , the l -expansion of the wave function were carried out up to l max = 10 while the charge density was Fourier expanded up to G max = 14 (Ryd) 1/2 . In order to achieve energy eigenval- 0375-9601/$ – see front matter  2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physleta.2007.10.077