Computational Materials Science 50 (2010) 2–5 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci Influence of doped rare earth elements on electronic properties of the R0.25Ca0.75MnO3 systems Nguyen Hoang Linh a,*, Nguyen Thuy Trang a, Nguyen Tien Cuong a, Pham Huong Thao b, Bach Thanh Cong a a b Faculty of Physics, Hanoi University of Science, Vietnam National University – Hanoi, Vietnam Faculty of Physics, Hue University of Education, Hue University, Vietnam a r t i c l e i n f o Article history: Received 29 October 2009 Received in revised form 25 February 2010 Accepted March 2010 Available online April 2010 Keywords: Calcium manganese Density functional theory Doping compound Doped rare – earth elements a b s t r a c t The influence of doped rare earth elements on the some electronic properties of perovskite systems R0.25Ca0.75MnO3 (R = La, Nd, Eu, Tb, Ho, Y) is investigated using the density functional theory with Dmol3 code The density of states, band structure, tolerance factor and Jahn–Teller splitting energy were calculated By doping the different rare earth elements, the systems show different changing in the crystal structure, hopping amplitude, and electrical resistivity Among these doping compounds, the Eu0.25Ca0.75MnO3 exhibits the strongest structural change corresponding to the largest Jahn–Teller splitting Ó 2010 Elsevier B.V All rights reserved Introduction During recent decade, the rare earth-doped calcium manganese perovskites have attracted much attention due to their exotic behaviors, such as the colossal magnetoresistance (CMR), the large magnetocaloric effects, as well as their potential for applications in electronics industry [1] Like other classic perovskites, the pure CaMnO3 crystal has a perfect perovskite structure with cubic symmetry belonged to Pnma space group The lattice parameter of the cubic CaMnO3, a = 3.75 Å, was determined by Wollan and Koehler [2] Moreover, CaMnO3 exhibits a G-type antiferromagnetic insulator with the band structure as a Mott insulator [1] Doping with rare earth element makes the ion concentration ratio between Mn3+/Mn4+ altering from to This induces a big change in the conductivity of the doped systems For example, Sousa et al found that by substituting Holmium for Calcium, Ho1ÀxCaxMnO3 exhibit a significant decrease in the electrical conductivity and the metal–insulator transition temperature increases with increasing of the holmium concentration [3] In [4], the melting of the charge ordering state by Ruthenium doping for manganese in calcium-praseodymium perovskite was also observed By using the density functional theory (DFT), this paper concentrated to study on electronic properties of the typical rare earthdoped calcium manganese oxides with the general chemical for- * Corresponding author Tel.: +84 912489852 E-mail addresses: linknh@gmail.com (N.H Linh), congbt@vnu.edu.vn (B.T Cong) 0927-0256/$ - see front matter Ó 2010 Elsevier B.V All rights reserved doi:10.1016/j.commatsci.2010.03.002 mula, R0.25Ca0.75MnO3 (R = La, Nd, Eu, Tb, Ho, Y) The calculations were effectively carried out using the Dmol3 package The pure CaMnO3 unit cell has been constructed with the symmetric standard coordinates of atoms as following: Ca (0, 0, 0); Mn (1/2, 1/2, 1/2); O1 (0, 1/2, 1/2); O2 (1/2, 0, 1/2); O3 (1/2, 1/2, 0) Then, the modeling bulk crystals of the R0.25Ca0.75MnO3 systems were built by replacing ion Ca2+ with ion R3+ at the symmetric coordinates as showed in the supercell with the size   given in Fig In the present study, we chose Perdew–Wang correlation functional (PW91) of generalized gradient approximation (GGA) A spin restricted calculation (treating separately for spin up and spin down electrons) for a system having odd number of electrons is also applied K-point was chosen with   for pure CaMnO3 model and   for doping model Fine orbital cutoff quality was set as default of DMol3 code: 5.5 Å for pure CaMnO3 model and 5.8 Å for doping model The accuracy of these calculations is improved by all electron relativistic treatment for cores Results and discussion 2.1 CaMnO3 bulk structure Dependence of the total energy on the lattice parameter of the cubic CaMnO3 bulk crystal was calculated in Hatree unit (1 Ha = 27.221 eV) and plotted in Fig From this figure the optimized lattice constant, a = 3.75 Å, was founded This value is in N.H Linh et al / Computational Materials Science 50 (2010) 2–5 Fig The modeling supercell of doped R0.25Ca0.75MnO3 perovskite compounds (R = La, Nd, Eu, Tb, Ho, and Y) Fig Density of spin states of ion Mn4+ in the cubic CaMnO3 with Fermi levels was shifted to zero (dashed line) Where, the blue and red lines stand for the spin-up and the spin-down states of the system CaMnO3, respectively Black and green lines stand for the spin up and spin down of d-level of ion Manganese (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) Fig The total energy as function of lattice parameter of the cubic CaMnO3 agreement with previous experimental and theoretical studies [2,3] The model of Goodenough, which is known as semi-covalent exchange interaction model, shows clearly antiferromagnetic state of CaMnO3 [5] In this compound, the antiferromagnetic coupling between magnetic manganese ions results from their indirect interaction via intermediate oxygen ion with fully occupied p-orbi- tal So, the spin coupling of two nearest neighboring manganese ions was indirectly oriented by two anti-parallel spins in the full orbital of the neighboring oxygen ion Fig shows the density of spin states of ion Mn4+ in the bulk CaMnO3 at the lattice parameter a = 3.75 Å With spin-up and spin-down states of ion Mn4+ distributed equally at the energy levels, it is clearly seen that the system is antiferromagnetic one This also agreed with the density of spin states of total systems The insulating properties show clearly in the band structure with the band gap estimated 0.038 Ha ($1.034 eV) 2.2 Rare earth-doped calcium manganese perovskite compounds The lattice constants of doping compounds are optimized by plotting total energy as a function of lattice parameter In Fig 4, the dependences of total energy on lattice parameter of La-doped and Ne-doped compounds are showed as typical examples The Fig Lattice optimization for the La (a) and Nd (b) doped perovskites 4 N.H Linh et al / Computational Materials Science 50 (2010) 2–5 Fig Dependence of the tolerance factor f (a), hoping parameter t (b) and Jahn–Teller energy (c) on the rare earth ions radii for the doping R0.25Ca0.75MnO3 compounds (R = La, Nd, Eu, Tb, Ho, Y) similar calculations for other compounds were carried out by the same way The influence of rare earth elements on the structure change is AÀO > examined through the tolerance factor: f ¼ pffiffi2