Bulk and surface electronic structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Li</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O

Liu, Lizhong; Henrich, Victor E.; Ellis, W. P.; Shindo, Isamu

doi:10.1103/physrevb.54.2236

Cited by 63 publications

(46 citation statements)

References 25 publications

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“…In the density of the O(2p)-states of layer 5, a structure typical of the volume N(E), appears. This is consistent with the experimental data [4], where it is shown that in the low-energy part of the O(2p)-region of photoemission spectrum, the intensity increases with increasing photon energy, and hence the depth of photoelectron emission.…”

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“…Such surfaces often prove relatively stable [2]. Oxides of alkali metals were investigated both by experimental and theoretical methods, however, the electronic structure and geometry relaxation of the (111) surface were studied only for Li 2 O [3,4]. In so doing, in the framework of the Hartree-Fock method, a model of a 2-layer thick plate was applied [3], which is insufficient for studying surfaces.…”

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The structure and electronic properties of the (111)-surface of alkali metal oxides

2011

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Under normal conditions, М 2 О oxides (M = Li, Na, K) crystallize into a structure of the antifluorite type with one formula unit (N = 1) [1]. Each (111) surface layer of the М 2 О oxide consists of three charged atomic layers M-O-M. Such surfaces often prove relatively stable [2]. Oxides of alkali metals were investigated both by experimental and theoretical methods, however, the electronic structure and geometry relaxation of the (111) surface were studied only for Li 2 O [3,4]. In so doing, in the framework of the Hartree-Fock method, a model of a 2-layer thick plate was applied [3], which is insufficient for studying surfaces. Thus, the surface of oxides is poorly understood.In this work, calculations for М 2 О are performed using the CRYSTAL06 package [5]. In the calculations, use was made of the basis of linear combinations of atomic orbitals (LCAO) and the hybrid functional B3PW [6]. The bases 6-411G, 6-1G, 8-511G, and 86-511G were used for an oxygen atom and Li-, Na-, and K cations, respectively [7]. In so doing, the calculated lattice constants in the volume deviate from the experimental values [1] only by 0.18, 0.46 and 1.8% for Li 2 O, Na 2 O, and K 2 O, respectively. In addition, the experimental oxygen atom charge (-1.90 |e|) for Li 2 O is very well reproduced (-1.897 |e|) [8]). The surface was modeled by a two-dimensional plate (2D), which was "cut out" from a three-dimensional crystal (3D). The Cartesian axes were arranged in such a way that the Z axis was perpendicular to the examined (hkl) surface. The surface is defined as a set of atomic layers, whose properties are different from the bulk ones, and each layer is determined by the atoms with fixed Z. A two-dimensional unit cell was chosen in such a way that the properties of the middle layer reproduced the volume properties with an accuracy of 0.2%. The surface energy was calculated using the formula Е surf (n) = (Е 2D -nE 3D )/2∆S surf , where Е 2D is the energy of a 2D-unit cell of the plate, Е 3D is the energy of a 3D-unit cell of the crystal, n = N 2D /N 3D , and ∆S surf is the area of the basis of a 2D unit cell. Table 1 shows the atomic charges and displacements of atomic layers of the M 2 O (111) surface caused by surface relaxation. The numbering of atomic layers starts from the topmost layer. Fourteen atomic layers were sufficient to consider surface properties. Displacements of oxygen atoms in Li 2 O reach a maximum value of 1.08% (layer 2) and those for lithium atoms are 0.96% (layer 3). Then, the displacements decrease into the depth, so that for the twelfth layer, they are only 0.16%, which is an order lower than the relaxation for layer 3. The displacements of layers of sodium and potassium oxides decrease in a similar way, while with increasing atomic number of the cation, the surface atoms undergo greater relaxation. The changes of atomic charges in the upper layers of oxide surface relative to the volume increase with the atomic number of the cation, but they do not exceed 0.005, 0.010, and 0.012 |e|, respectively. Starting fro...

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The structure and electronic properties of the (111)-surface of alkali metal oxides

2011

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“…Owing to these usefulness and interest, both theoretical and experimental investigations aimed at understanding the conduction mechanism [4], the lattice dynamics [5,6] and the defect formation [7] have been carried out by many workers. The electronic structures of Li 2 O have been studied with ab initio self-consistent calculations [8 to 10] and embedded-cluster calculation [11], and also investigated by using photoemission and electron-energy-loss spectroscopies [12]. Our recent reflection experiment using high-quality single crystals [13] has found the lowest exciton band to be located at 7.02 eV.…”

Section: Introductionmentioning

confidence: 98%

Intrinsic Luminescence from Li2O Crystals Excited in the Exciton-Band Region

Itoh

Murakami

Ishii

1999

phys. stat. sol. (b)

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Photoluminescence of lithium oxide (Li2O) has been studied under the excitation with UV light in the fundamental absorption region at low temperatures. Two bands appear at 3.70 and 4.75 eV. The 3.70 and 4.75 eV bands are stimulated on the low‐ and high‐energy sides of the exciton reflection band peaking at 7.02 eV, respectively. An interesting fact is that there appears no luminescence under the above‐gap excitation. The 4.75 eV band is ascribed to radiative decay of self‐trapped excitons, and the 3.70 eV band is related to unavoidably existing defects or impurities. Both a broadening of the line width and a quenching of the intensity of the 4.75 eV band are also investigated in the temperature range 9 to 300 K. The present result is discussed in comparison with the theoretical model of the self‐trapped exciton in this material.

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“…This is rather unexpected, and our experimental values also fall below previous measurements. However, previous data are generally derived from the width of the DOS measured by photoemission 10,14,15 , and there is no generally accepted rule for determining the bandwidth by this method. As Erwin and Lin 40 point out, care must be exercised in comparing such bandwidths with other data because they may overestimate the true width.…”

Section: B Trends In the Oxide Valence Band Structurementioning

confidence: 99%

“…Ultraviolet (UPS) and x-ray photoemission spectroscopy (XPS) have been used to probe oxidation of Li [1][2][3] , Na 4,5 or K 1,3,5,6 and the absorption of oxygen onto potassium covered surfaces of Pt, Fe and ZrC 7 . The core levels have been measured in electron emission by Barrie and Street 8 , and only recently densities of states in the valence and core regions of Li 2 O have been reported by Tanaka et al 9 and Liu et al 10 using XPS and UPS. A number of optical 11 , x-ray 12,13 and photoemission measurements 14,15 for the group II oxides have been available in the literature for some time, and provide data on only certain aspects of the electronic structure, such as special point energies.…”

Section: Introductionmentioning

confidence: 99%