Influence of temperature on the microstructure and phase transition of a CaSiO3 bulk model

This paper studies the influence of temperature 500 K, 1500 K, 2500 K, 3500 K and 4000 K on the microstructure and phase transition of a CaSiO3 bulk model using the Molecular Dynamics method with the Born-Mayer pair interaction potential and periodic boundary conditions.
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Influence of temperature on the microstructure and phase transition of a CaSiO3 bulk model JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2016-0036 Mathematical and Physical Sci., 2016, Vol. 61, No. 7, pp. 88-97 This paper is available online at http://stdb.hnue.edu.vn INFLUENCE OF TEMPERATURE ON THE MICROSTRUCTURE AND PHASE TRANSITION OF A CaSiO3 BULK MODEL Nguyen Trong Dung, Nguyen Thi Ha and Nguyen Chinh Cuong Faculty of Physics, Hanoi National University of Education Abstract. This paper studies the influence of temperature 500 K, 1500 K, 2500 K, 3500 K and 4000 K on the microstructure and phase transition of a CaSiO3 bulk model using the Molecular Dynamics method with the Born-Mayer pair interaction potential and periodic boundary conditions. The obtained samples were analyzed through the radial distribution function (RDF), and the coordination number, angle distribution, size, energy and phase transition were determined using the relation between temperature and energy. The calculated results show that temperature influences the microstructure and phase transition of a CaSiO3 bulk model. In addition, the samples at different temperatures have the different couplings Si-Si, Si-O, O-O, Si-Ca, O-Ca and Ca-Ca and the different coordination numbers SiO4 , SiO5 , SiO6 , CaO3 , CaO4 , CaO5 , CaO6 , CaO7 , CaO8 and CaO9 . Keywords: Temperature, microstructure, Molecular Dynamics, CaSiO3 bulk model.1. Introduction In recent years, an increasing number of studies on CaSiO3 perovskite have been done.CaSiO3 is not stable at high pressure [1, 2]. It is an important component which characterizesthe versatility of glass [3]. In studying the microstructure of CaSiO3 , many methods can beused, including X-ray diffraction [4] and EXAFS spectroscopic analysis [5, 6]. In particular, thecouplings 17O and 29Si have been detected in the material using neutron diffraction [7, 8]. Theresults show that in this material there are two types of isotopes: A silica tetrahedral lattice with Caas the lattice controller and Ca-O with coordination number 6. Neutron diffraction results showthat there are differences in the isotope substitution for the Ca-Ca correlation. X-ray diffractionand neutron diffraction results [9, 10] for CaSiO3 crystal are similar to the above results. According to simulation results [11], the Si-O couplings are 1.7 A ˚ and the coordinationnumbers of Si-O are 4 and 7 [12]. The phase transition in CaSiO3 perovskite was determinedexperimentally and theoretically [13]. According to the results for CaO1−x (SiO2 )x , the phasetransition temperature depends on the concentration of SiO2 and the research methods. Forexample, at x ≈ 0.33, the phase transition temperature is 1978 K; at x ≈ 0.4, the phase transitiontemperature is 1709 K and at x ≈ 0.5, the phase transition temperature is 1817 K. [14]. Fromexperimental data, the phase transition temperature is 1873 K [15]. The distance between couplingsis 1.7 A˚ for Si-O [15], 1.61 A ˚ for Si-O, 2.6 A˚ for O-O [16] and 2.48 A ˚ for Ca-O [17]. We can seeReceived August 29, 2016. Accepted September 26, 2016.Contact Nguyen Trong Dung, e-mail address: dungntsphn@gmail.com88 Influence of temperature on the microstructure and phase transition of a CaSiO3 bulk modelthat it is difficult to determine the property of a material which is not stable in structure. In thispaper, the influence of temperature on the microstructure and phase transition of a CaSiO3 bulkmodel was studied using the Molecular Dynamics method.2. Content2.1. Calculation method The CaSiO3 bulk model with 5000 atoms at T = 500 K, 1000 K, 1500 K, 2000 K, 2500K, 3000 K and 4000 K was studied using the Molecular Dynamics method with Born-Mayer pairinteraction potential (1) and periodic boundary conditions [18]. Cij Uij (r) = Aij exp(−Bij rij ) − 6 (2.1) rijwhere Uij (r) is the pair interaction potential in eV units, rij is the distance between atoms in A ˚ ˚ units and the coefficients Aij , Bij and Cij are determinedunits, rcut is the disconnect radius in Aexperimentally with the use of elastic modules and the lattice constant as shown in Table 1. Table 1. The coefficients of Born-Mayer pair interaction potential used in the CaSiO3 bulk model Si-Si Si-O O-O Si-Ca O-Ca Ca-Ca Aij (eV) 5006070.785 7363.700 1621.734 39991 ...