DOCSLIB.ORG

Structure and Basic Magnetic Properties of the Honeycomb Lattice Compounds Na2co2teo6 and Na3co2sbo6 L

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Structure and Basic Magnetic Properties of the Honeycomb Lattice Compounds Na2co2teo6 and Na3co2sbo6 L ARTICLE IN PRESS Journal of Solid State Chemistry 180 (2007) 1060–1067 www.elsevier.com/locate/jssc Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6 L. Viciua,Ã, Q. Huangb, E. Morosana, H.W. Zandbergenc, N.I. Greenbauma, T. McQueena, R.J. Cavaa aDepartment of Chemistry, Princeton University, Princeton NJ 08544, USA bNIST Center for Neutron Research, NIST, Gaithersburg, MD 20899, USA cNational Centre for HREM, Department of Nanoscience, Delft Institute of Technology, Al Delft, The Netherlands Received 26 September 2006; received in revised form 15 December 2006; accepted 2 January 2007 Available online 14 January 2007 Abstract The synthesis, structure, and basic magnetic properties of Na2Co2TeO6 and Na3Co2SbO6 are reported. The crystal structures were determined by neutron powder diffraction. Na2Co2TeO6 has a two-layer hexagonal structure (space group P6322) while Na3Co2SbO6 has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co2+ and Te6+/Sb5+ ions in the ab plane such that the Co2+ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na2Co2TeO6 and Na3Co2SbO6 display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na3Co2SbO6. r 2007 Published by Elsevier Inc. Keywords: Honeycomb lattice; Layered cobalt compounds; Antiferromagnetic ordering 1. Introduction ions have a triangular planar lattice, considered an important factor in driving the properties in these phases. The study of the magnetic properties of low dimensional One variant of the triangular lattice is the honeycomb systems has played an important role in condensed matter geometry, where 1/3 of the sites of a triangular lattice are physics [1]. The understanding of both the theoretical non-magnetic. Compounds with the magnetic ions in this models and the concepts of low dimensional magnets geometry have manifested interesting properties such as gained momentum with the discovery of high Tc super- spin-glass behavior [10], spin-flop transitions [11] and even conductivity in cuprates, where the magnetic ions are superconductivity [12]. Here we report the synthesis, arranged in square planes [2]. Also of recent interest have structural and magnetic characterization of two Co-based been triangle-based geometries: when populated with compounds, Na2Co2TeO6 and Na3Co2SbO6, in which the antiferromagnetically coupled magnetic atoms, frustration Co ions are arranged in a honeycomb lattice. Na3Co2SbO6 of the low temperature magnetic states can occur due to was recently described as being trigonal [13] but no other conflicting near neighbor spin interactions [3]. In this information related to the synthesis, structural or physical category, NaxCoO2 represents one of the richest systems of property characterization of this phase is available. The Te- current interest [4–8]. The layered structures of the based compound has not been previously reported. NaxCoO2 phases consist of planes of edge-sharing cobal- t–oxygen octahedra interleaved with Na ions [9]. The Co 2. Experimental à Corresponding author. Fax: 609 258 6746. Na2Co2TeO6 and Na3Co2SbO6 were prepared by mixing E-mail address: [email protected] (L. Viciu). Na2CO3 (Alfa, 99.5%) and Co3O4 (Alfa, 99.7%) with TeO2 0022-4596/$ - see front matter r 2007 Published by Elsevier Inc. doi:10.1016/j.jssc.2007.01.002 ARTICLE IN PRESS L. Viciu et al. / Journal of Solid State Chemistry 180 (2007) 1060–1067 1061 (JMC, 99.9995%) or Sb2O4 (Sb2O5 Alfa, 99.5%, annealed pattern of Na2Co2TeO6 was indexed with a hexagonal cell for 12 h at 1000 1C in air to prepare Sb2O4). The Co:(Sb,Te) in the space group P6322 (No.182), while that of ratio was stoichiometric, but 20% excess Na2CO3 was Na3Co2SbO6 was indexed with a centered monoclinic cell added to compensate for loss due to volatilization. The in the space group C2/m (No. 12). Structural analysis by mixtures were thoroughly ground, pressed into pellets the Rietveld method based on the powder neutron (f ¼ 13 mm) and annealed under flowing nitrogen as diffraction data was performed for both compounds. The follows: 8 days at 800 1C were necessary for Na2Co2TeO6 cell constants, as determined by powder neutron diffrac- with two intermediate grindings—one after 4 days and then tion, are presented in Tables 1 and 2.Na2Co2TeO6 displays another one after 2 days of subsequent annealing; a primitive, two-layer hexagonal structure, while Na3Co2 Na3Co2SbO6 was obtained after 2 days of thermal SbO6 has a single layer monoclinic structure, very similar treatment at 800 1C. In all cases, the furnace temperature to what is seen in Na3Cu2SbO6 [13]. was increased by 5 1C/min until the desired temperature The neutron powder diffraction pattern for Na2Co2TeO6 was reached. Slow cooling to room temperature after shows it to have no observable dimensional deviations reaction completion, 5 1C/min, was performed. The com- from hexagonal symmetry. Its honeycomb-based crystal pounds are both lightly pastel-colored, indicating that they structure was found to be very well described in space have large band gaps and no significant electrical group P6322. A classic two-layer structure, similar to that conductivity or Co mixed valency. of Na0.7CoO2 [9], but with a larger in-plane unit cell to The purity of the samples was analyzed by powder X-ray accommodate the honeycomb-type cobalt-tellurium order- diffraction using CuKa radiation and a diffracted beam ing, is found. The crystal structure is presented in Figs. 3a monochromator. Neutron diffraction data were collected and b. Two symmetry-independent Co ions within the on Na2Co2TeO6 and Na3Co2SbO6 at the NIST Center for honeycomb layer, one type of Te, one type of oxygen, and Neutron Research on the high resolution powder neutron three independent Na ion positions were found. Models in diffractometer (BT1) with monochromatic neutrons of which Co–Te intermixing was tested for the metal atom wavelength 1.5403 A˚produced by a Cu(311) monochro- sites did not yield significant mixing: the atoms are fully mator. Collimators with horizontal divergences of 150,200 ordered. Refinements were carried out with atoms of the and 70 of arc were used before and after the monochro- same type constrained to have the same thermal para- mator and after the sample, respectively. Data were meters. collected in the 2-y range of 3–1681 with a step size of The Na distribution between the honeycomb layers is 0.051. The structural parameters were refined using the highly disordered. The geometry of the oxygen array in the program GSAS [14] The sodium content in each sample planes neighboring the Na planes creates triangular was determined by the structure refinement, and was in prismatic sites for the Na, exactly as is found in two-layer 9 good agreement with that expected from nominal composi- NaxCoO2. In the NaxCoO2 structures, Na is found to tions. occupy triangular prisms of two types: one type that shares The magnetic properties were measured with a Quantum only edges with the metal octahedra in the planes above Design PPMS system. Zero field cooled (ZFC) and field and below, and one that shares faces with the metal cooled (FC) magnetization data were taken between 1.8 octahedra in the planes above and below. The same and 280 K in an applied field of 1 T. Field dependent situation is found for Na2Co2TeO6. In this case, though, magnetization data were recorded at 5 and 30 K for there are two types of face sharing possible, as the Na2Co2TeO6, and at 5, 8 and 12 K for Na3Co2SbO6. triangular prisms can share faces with one Co octahedron and one Te octahedron in the planes above and below, or 3. Results with two Co octahedra. The final refinements (Table 1) showed that the Na ions partially occupy all three types of The purity of the compounds was confirmed by X-ray available triangular prismatic sites, in different amounts: diffraction analysis. The powder neutron diffraction 71% of the Na are in the triangular prisms that share edges Table 1 ˚ ˚ ˚3 Crystallographic data for Na2Co2TeO6 in the space group P6322 (no. 182), a ¼ 5.2889(1)A, c ¼ 11.2149(4)A, volume ¼ 271.68(1) A ˚ Atom Wyckoff position xyzUiso  100 (A) Occ. Co(1) 2b 0 0 1/4 0.8(1) 1 Co(2) 2d 2/3 1/3 1/4 0.8(1) 1 Te 2c 1/3 2/3 1/4 0.9(1) 1 O12i 0.6432(6) À0.0252(4) 0.3452(1) 1.50(4) 1 Na(1) 12i 0.24(1) 0.65(2) À0.026(3) 0.8(3) 0.081(7) Na(2) 2a 0 0 0 0.8(3) 0.11(3) Na(3) 12i 0.702(3) 0.066(2) À0.006(2) 0.8(3) 0.234(6) 2 2 w ¼ 1.39; wRp ¼ 6.53; Rp ¼ 5.05; RðF Þ¼8:4%. ARTICLE IN PRESS 1062 L. Viciu et al. / Journal of Solid State Chemistry 180 (2007) 1060–1067 Table 2 ˚ ˚ ˚ Crystallographic data for Na3Co2SbO6 in the space group C2/m (no. 12), a ¼ 5.3681(2) A, b ¼ 9.2849(4) A, c ¼ 5.6537(2) A, b ¼ 108.506(4)1, volume ¼ 267.22(2) A˚3 ˚2 Atom Wyckoff position xyzUiso  100 (A ) Occ. Co 4g 0 2/3 0 0.23(12) 1 Sb 2a 0 0 0 1.86(17) 1 O(1) 8j 0.2744(8) 0.3410(3) 0.7971(5) 1.25(2) 1 O(2) 4i 0.2463(10) 0.5 0.2056(10) 1.25(2) 1 Na(1) 2d 0 0.5 0.5 1.58(5) 1 Na(2) 4h 0.5 0.3296(9) 0.5 1.58(5) 1 2 2 w ¼ 1.01; wRp ¼ 5.31%; Rp ¼ 4.31%; R(F ) ¼ 7.57%.
Load more

Recommended publications
  • Uniform Panoploid Tetracombs
    Uniform Panoploid Tetracombs George Olshevsky TETRACOMB is a four-dimensional tessellation. In any tessellation, the honeycells, which are the n-dimensional polytopes that tessellate the space, Amust by definition adjoin precisely along their facets, that is, their ( n!1)- dimensional elements, so that each facet belongs to exactly two honeycells. In the case of tetracombs, the honeycells are four-dimensional polytopes, or polychora, and their facets are polyhedra. For a tessellation to be uniform, the honeycells must all be uniform polytopes, and the vertices must be transitive on the symmetry group of the tessellation. Loosely speaking, therefore, the vertices must be “surrounded all alike” by the honeycells that meet there. If a tessellation is such that every point of its space not on a boundary between honeycells lies in the interior of exactly one honeycell, then it is panoploid. If one or more points of the space not on a boundary between honeycells lie inside more than one honeycell, the tessellation is polyploid. Tessellations may also be constructed that have “holes,” that is, regions that lie inside none of the honeycells; such tessellations are called holeycombs. It is possible for a polyploid tessellation to also be a holeycomb, but not for a panoploid tessellation, which must fill the entire space exactly once. Polyploid tessellations are also called starcombs or star-tessellations. Holeycombs usually arise when (n!1)-dimensional tessellations are themselves permitted to be honeycells; these take up the otherwise free facets that bound the “holes,” so that all the facets continue to belong to two honeycells. In this essay, as per its title, we are concerned with just the uniform panoploid tetracombs.
    [Show full text]
  • On the Application of the Honeycomb Conjecture to the Bee's Honeycomb
    On the Application of the Honeycomb Conjecture to the Bee’s Honeycomb∗y Tim Räzz July 29, 2014 Abstract In a recent paper, Aidan Lyon and Mark Colyvan have proposed an explanation of the structure of the bee’s honeycomb based on the mathematical Honeycomb Conjecture. This explanation has instantly become one of the standard examples in the philosophical debate on mathematical explanations of physical phenomena. In this critical note, I argue that the explanation is not scientifically adequate. The reason for this is that the explanation fails to do justice to the essen- tially three-dimensional structure of the bee’s honeycomb. Contents 1 Introduction 2 2 Lyon’s and Colyvan’s Explanation 2 3 Baker: A Philosophical Motivation 3 4 Why the Explanation Fails 4 4.1 The Explanation is Incomplete . .4 4.2 The Honeycomb Conjecture Is (Probably) Irrelevant . .7 ∗Acknowledgements: I am grateful to Mark Colyvan, Matthias Egg, Michael Esfeld, Martin Gasser, Marion Hämmerli, Michael Messerli, Antoine Muller, Christian Sachse, Tilman Sauer, Raphael Scholl, two anonymous referees, and the participants of the phi- losophy of science research seminar in the fall of 2012 in Lausanne for discussions and comments on previous drafts of this paper. The usual disclaimer applies. This work was supported by the Swiss National Science Foundation, grants (100011-124462/1), (100018- 140201/1) yThis is a pre-copyedited, author-produced PDF of an article accepted for publication in Philosophia Mathematica following peer review. The definitive publisher-authenticated version, Räz, T. (2013): On the Application of the Honeycomb Conjecture to the Bee’s Honeycomb.
    [Show full text]
  • Designing Modular Sculpture Systems
    Bridges 2017 Conference Proceedings Designing Modular Sculpture Systems Christopher Carlson Wolfram Research, Inc 100 Trade Centre Drive Champaign, IL, 61820, USA E-mail: [email protected] Abstract We are interested in the sculptural possibilities of closed chains of modular units. One such system is embodied in MathMaker, a set of wooden pieces that can be connected end-to-end to create a fascinating variety of forms. MathMaker is based on a cubic honeycomb. We explore the possibilities of similar systems based on octahedral- tetrahedral, rhombic dodecahedral, and truncated octahedral honeycombs. Introduction The MathMaker construction kit consists of wooden parallelepipeds that can be connected end-to-end to make a great variety of sculptural forms [1]. Figure 1 shows on the left an untitled sculpture by Koos Verhoeff based on that system of modular units [2]. MathMaker derives from a cubic honeycomb. Each unit connects the center of one cubic face to the center of an adjacent face (Figure 1, center). Units connect via square planar faces which echo the square faces of cubes in the honeycomb. The square connecting faces can be matched in 4 ways via 90° rotation, so from any position each adjacent cubic face is accessible. A chain of MathMaker units jumps from cube to adjacent cube, adjacent units never traversing the same cube. A variant of MathMaker called “turned cross mitre” has units whose square cross-sections are rotated 45° about their central axes relative to the standard MathMaker units (Figure 1, right). Although the underlying cubic honeycomb structure is the same, the change in unit yields structures with strikingly different visual impressions.
    [Show full text]
  • Polyhedra and Packings from Hyperbolic Honeycombs
    Polyhedra and packings from hyperbolic honeycombs Martin Cramer Pedersena,1 and Stephen T. Hydea aDepartment of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra ACT 2601, Australia Edited by Robion C. Kirby, University of California, Berkeley, CA, and approved May 25, 2018 (received for review November 29, 2017) We derive more than 80 embeddings of 2D hyperbolic honey- Disc Packings and Triangular Patterns combs in Euclidean 3 space, forming 3-periodic infinite polyhedra The density of 2D hard disc packing is characterized by the ratio with cubic symmetry. All embeddings are “minimally frustrated,” of the total area of the packed objects to the area of the embed- formed by removing just enough isometries of the (regular, ding space. Thus, the hexagonal “penny packing” of equal discs but unphysical) 2D hyperbolic honeycombs f3, 7g, f3, 8g, f3, 9g, 2 realizes the maximal packing density in the plane, E (24, 25). f3, 10g, and f3, 12g to allow embeddings in Euclidean 3 space. Dense packings of equal discs on the surface of the 2 sphere, Nearly all of these triangulated “simplicial polyhedra” have sym- 2, are more subtle, since the sphere’s finite area means that metrically identical vertices, and most are chiral. The most sym- S optimal solutions depend on the disc radius. The formal defini- metric examples include 10 infinite “deltahedra,” with equilateral tion of packing density for equal discs in the third homogeneous triangular faces, 6 of which were previously unknown and some 2 of which can be described as packings of Platonic deltahedra. We 2D space—the hyperbolic plane, H —is also complicated by the describe also related cubic crystalline packings of equal hyper- nature of that space.
    [Show full text]
  • This Is a Set of Activities Using Both Isosceles and Equilateral Triangles
    This is a set of activities using both Isosceles and Equilateral Triangles. 3D tasks Technical information This pack includes 25 Equilateral Triangles and 25 Isosceles Triangles. You will also need a small tube of Copydex. If you are new to making models with Copydex we suggest you start by watching www.atm.org.uk/Using-ATM-MATs Different polyhedra to make Kit A: 4 Equilateral Triangle MATs. Place one triangle on your desk and join the other three triangles to its three sides, symmetrically. Now add glue to one edge of each of the three added triangles so that all can be joined into a polyhedron This is your first polyhedron. Kit B: 3 Isosceles triangles and 1 equilateral triangle Kit C: 4 Isosceles triangles Kit D: 6 Equilateral Triangles Kit E: 6 Isosceles Triangles Kit F: 3 Equilateral and 3 Isosceles Triangles. (are there different possible polyhedra this time?) Kit G: 8 Equilateral Triangles. One possibility is a Regular Octahedron, but is there more than one Octahedron? Kit H: 4 Equilateral and 4 Isosceles Triangles (are there different possible polyhedra this time?) Kit I: 2 Equilateral Triangles and 6 Isosceles Triangles Kit J: Go back to the Regular Octahedron (from Kit G) and add a Regular Tetrahedron to one of its faces, then add another … until four have been added. Keep track (in a table) of how many faces and vertices the Regular Octahedron and the next four polyhedra have. Hint: if you spaced the added Tetrahedra equally around the Octahedron you will find a bigger version of a previously made solid.
    [Show full text]
  • Cannonballs and Honeycombs, Volume 47, Number 4
    fea-hales.qxp 2/11/00 11:35 AM Page 440 Cannonballs and Honeycombs Thomas C. Hales hen Hilbert intro- market. “We need you down here right duced his famous list of away. We can stack the oranges, but 23 problems, he said we’re having trouble with the arti- a test of the perfec- chokes.” Wtion of a mathe- To me as a discrete geometer Figure 1. An matical problem is whether it there is a serious question be- optimal can be explained to the first hind the flippancy. Why is arrangement person in the street. Even the gulf so large between of equal balls after a full century, intuition and proof? is the face- Hilbert’s problems have Geometry taunts and de- centered never been thoroughly fies us. For example, what cubic tested. Who has ever chatted with about stacking tin cans? Can packing. a telemarketer about the Riemann hy- anyone doubt that parallel rows pothesis or discussed general reciprocity of upright cans give the best arrange- laws with the family physician? ment? Could some disordered heap of cans Last year a journalist from Plymouth, New waste less space? We say certainly not, but the Zealand, decided to put Hilbert’s 18th problem to proof escapes us. What is the shape of the cluster the test and took it to the street. Part of that prob- of three, four, or five soap bubbles of equal vol- lem can be phrased: Is there a better stacking of ume that minimizes total surface area? We blow oranges than the pyramids found at the fruit stand? bubbles and soon discover the answer but cannot In pyramids the oranges fill just over 74% of space prove it.
    [Show full text]
  • Families of Tessellations of Space by Elementary Polyhedra Via Retessellations of Face-Centered-Cubic and Related Tilings
    PHYSICAL REVIEW E 86, 041141 (2012) Families of tessellations of space by elementary polyhedra via retessellations of face-centered-cubic and related tilings Ruggero Gabbrielli* Interdisciplinary Laboratory for Computational Science, Department of Physics, University of Trento, 38123 Trento, Italy and Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA Yang Jiao† Physical Science in Oncology Center and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, USA Salvatore Torquato‡ Department of Chemistry, Department of Physics, Princeton Center for Theoretical Science, Program in Applied and Computational Mathematics and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, USA (Received 7 August 2012; published 22 October 2012) The problem of tiling or tessellating (i.e., completely filling) three-dimensional Euclidean space R3 with polyhedra has fascinated people for centuries and continues to intrigue mathematicians and scientists today. Tilings are of fundamental importance to the understanding of the underlying structures for a wide range of systems in the biological, chemical, and physical sciences. In this paper, we enumerate and investigate the most comprehensive set of tilings of R3 by any two regular polyhedra known to date. We find that among all of the Platonic solids, only the tetrahedron and octahedron can be combined to tile R3. For tilings composed of only congruent tetrahedra and congruent octahedra, there seem to be only four distinct ratios between the sides of the two polyhedra. These four canonical periodic tilings are, respectively, associated with certain packings of tetrahedra (octahedra) in which the holes are octahedra (tetrahedra).
    [Show full text]
  • Self-Assembly of a Space-Tessellating Struc- Ture in the Binary System of Hard Tetrahedra and Octahedra†
    Electronic Supplementary Material (ESI) for Soft Matter. This journal is © The Royal Society of Chemistry 2016 Supplementary Information: Self-assembly of a space-tessellating struc- ture in the binary system of hard tetrahedra and octahedra† A. T. Cadotte,a‡, J. Dshemuchadse,b‡ P. F. Damasceno,a§ R. S. Newman,b and S. C. Glotzer∗a;b;c;d Structure analysis with bond order diagrams 4-fold 3-fold 2-fold The crystal structures observed in this study were an- alyzed primarily by visual inspection. However, bond- orientational order diagrams (BODs) 1 were also found to 2 be instructive, especially when investigating structural sub- -OT c tleties. In the binary structure, the BODs were also gener- ated both for the mixture of polyhedra and for tetrahedra and octahedra separately. In the binary crystal, the centers of the tetrahedra form a simple cubic lattice, and the octa- (T) hedra form a face-centered cubic lattice. The BODs of the 2 binary structure and the octahedra packings are shown in -OT Fig. S1, the ones of the dodecagonal quasicrystal in Fig. S2. c The quasicrystal of tetrahedra has a particular signature in the BOD, resembling a cylinder and resulting in dark spots aligned with the 12-fold axis of the dodecagonal structure. (O) Quasicrystal binary-crystal coexistence 2 -OT Small numbers of octahedra that are present in a sim- c ulation of mainly tetrahedra have a preferred alignment within the quasicrystal. In some cases, they form five- rings, alternating with pentagonal bipyramids of tetrahe- dra, similar to a model of dodecagonal Al–Mn 2–4, as shown -O in Fig.
    [Show full text]
  • Math.GT] 29 Nov 2017 Embedded in Skeletons (Or Scaffoldings) of the Canonical Cubical Honeycombs of an Euclidean Or Hyperbolic Space
    Topological surfaces as gridded surfaces in geometrical spaces. Juan Pablo D´ıaz,∗ Gabriela Hinojosa, Alberto Verjosvky, y November 27, 2017 Abstract In this paper we study topological surfaces as gridded surfaces in the 2-dimensional scaffolding of cubic honeycombs in Euclidean and hy- perbolic spaces. Keywords: Cubulated surfaces, gridded surfaces, euclidean and hyperbolic honeycombs. AMS subject classification: Primary 57Q15, Secondary 57Q25, 57Q05. 1 Introduction The category of cubic complexes and cubic maps is similar to the simplicial category. The only difference consists in considering cubes of different di- mensions instead of simplexes. In this context, a cubulation of a manifold is a cubical complex which is PL homeomorphic to the manifold (see [4], [7], [12]). In this paper we study the realizations of cubulations of manifolds arXiv:1703.06944v2 [math.GT] 29 Nov 2017 embedded in skeletons (or scaffoldings) of the canonical cubical honeycombs of an euclidean or hyperbolic space. In [1] it was shown the following theorem: ∗This work was supported by FORDECYT 265667 (M´exico) yThis work was partially supported by CONACyT (M´exico),CB-2009-129280 and PA- PIIT (Universidad Nacional Aut´onomade M´exico)#IN106817. 1 Theorem 1.1. Let M; N ⊂ Rn+2, N ⊂ M, be closed and smooth subman- ifolds of Rn+2 such that dimension (M) = n + 1 and dimension (N) = n. Suppose that N has a trivial normal bundle in M (i.e., N is a two-sided hy- persurface of M). Then there exists an ambient isotopy of Rn+2 which takes M into the (n+1)-skeleton of the canonical cubulation C of Rn+2 and N into the n-skeleton of C.
    [Show full text]
  • Arxiv:1707.09780V1 [Cond-Mat.Mes-Hall] 31 Jul 2017 Not Only in Zigzag and Bearded Terminations, but Also in Arm- Chair Edges [10]
    Optical properties of honeycomb photonic structures Artem D. Sinelnik1, Mikhail V. Rybin2;3,∗ Stanislav Y. Lukashenko1, Mikhail F. Limonov2;3, and Kirill B. Samusev2;3 1Department of Nanophotonics and Metamaterials, ITMO University, St. Petersburg 197101, Russia 2Ioffe Institute, St. Petersburg 194021, Russia and 3Department of Dielectric and Semiconductor Photonics, ITMO University, St.Petersburg 197101, Russia (Dated: September 5, 2018) We study, theoretically and experimentally, optical properties of different types of honeycomb photonic struc- tures, known also as ‘photonic graphene’. First, we employ the two-photon polymerization method to fabricate the honeycomb structures. In experiment, we observe a strong diffraction from a finite number of elements, thus providing a unique tool to define the exact number of scattering elements in the structure by a naked eye. Then, we study theoretically the transmission spectra of both honeycomb single layer and 2D structures of parallel dielectric circular rods. When the dielectric constant of the rod materials " is increasing, we reveal that a two- dimensional photonic graphene structure transforms into a metamaterial when the lowest TE01 Mie gap opens up below the lowest Bragg bandgap. We also observe two Dirac points in the band structure of 2D photonic graphene at the K point of the Brillouin zone and demonstrate a manifestation of the Dirac lensing for the TM polarization. The performance of the Dirac lens is that the 2D photonic graphene layer converts a wave from point source into a beam with flat phase surfaces at the Dirac frequency for the TM polarization. I. INTRODUCTION is one of the physical phenomena that can be observed in the photonic as well as in the electronic realization of graphene.
    [Show full text]
  • Efficient Algorithm for Large Spectral Partitions
    Efficient algorithm for optimizing spectral partitions Beniamin Bogosel Abstract We present an amelioration of current known algorithms for optimal spectral partition- ing problems. The idea is to use the advantage of a representation using density functions while decreasing the computational time. This is done by restricting the computation to neighbourhoods of regions where the associated densities are above a certain threshold. The algorithm extends and improves known methods in the plane and on surfaces in di- mension 3. It also makes possible to make some of the first computations of volumic 3D spectral partitions on sufficiently large discretizations. 1 Introduction Recently many works were dedicated to the numerical study of spectral partitions in the plane and on surfaces in R3. These studies are motivated by the lack of an exact theoretical descrip- tion even in the simplest cases. One question which remains open is the study of the spectral honeycomb problem. What is the partition of the plane which asymptotically minimizes the sum of the first eigenvalues of the Dirichlet Laplacian of each cell? It was conjectured in [CL07] that the honeycomb partition is the best one. Big steps towards the proof of this conjecture were made in [BFVV17], where the authors prove that the spectral honeycomb conjecture is true among convex sets under the hypothesis that Polya’s conejcture holds for hexagons and a slightly weaker version holds for pentagons and heptagons. We recall that Polya’s conjecture states that among n-gons of fixed area, the regular one minimizes the first Dirichlet eigenvalue. Recent numerical simulations which confirm Polya’s conjecture can be found in [Bog15, Chap- ter 1].
    [Show full text]
  • Honeycombs & Hexagonal Geometry
    Introductory Module: Honeycombs are examples of well-adapted multi-purpose natural habitat structures that incorporate strength, versatility and material efficiency. LESSON: The Sweet ‘Bees-ness’ of Honeycomb and the Mathematics of Hexagonal Geometry Activity Purpose: 1) To develop an understanding that living things have structural features and adaptations that help them to survive in their environment and that growth and survival of living things are affected by physical conditions of their environment. 2) To investigate the properties of regular and irregular polygons and polyhedra and solve problems using geometric and algebraic reasoning. 3) To explore the application of algebraic expressions to describe geometric patterns, and solve problems by extending and applying the laws and properties of arithmetic to algebraic terms and expressions Student success criteria Questioning and predicting: With guidance, identify questions and problems associated with the geometry and structure of honeycombs that can be investigated mathematically and scientifically; and Make modelled predictions about honeycomb structures based on mathematical and scientific knowledge. Processing and analysing data and information: Summarise data from an investigation of honeycomb, use this understanding to identify relationships between natural structures and mathematical reasoning and draw conclusions based on findings Applying mathematical reasoning: Investigate and establish the properties of quadrilaterals and other polygons; regular and irregular tessellations and recurring geometric patterns Use algebra to express simple models describing geometric patterns and use algebraic expressions and mathematical reasoning to solve problems Communicating: Students will communicate their ideas and explanations on the geometry and structures of honeycombs using scientific written descriptions, geometric diagrams and simple algebraic models. Suggested Time: Approx.
    [Show full text]