Article pubs.acs.org/IC
Cite This: Inorg. Chem. 2019, 58, 8560−8569
New Members of SHG Active Dugganite Family, A3BC3D2O14 (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V): Synthesis, Structure, and Materials Properties Anupam Bhim,† Weiguo Zhang,‡ P. Shiv Halasyamani,*,‡ Jagannatha Gopalakrishnan,*,† and Srinivasan Natarajan*,† †
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore−560012, India Department of Chemistry, University of Houston, 112 Fleming Building, Houston, Texas 77204−5003, United States
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ABSTRACT: A family of compounds, A3BC3D2O14 (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V), with the Dugganite structure was prepared employing traditional solid-state chemistry methods. PXRD and Rietveld refinement studies indicate that the compounds are stabilized in P321 space group (no. 150). The compounds are found to be SHG active with values ranging from 1.9 to 15.0 × KDP. The compounds exhibit high dielectric constants and low loss in our studies. The noncentrosymmetry related properties of the new Dugganites were understood by band structure calculations. We also explored the present Dugganite-structured oxides for the development of new inorganic colored materials by substituting Co2+, Ni2+, Cu2+, and Fe3+ in place of Zn2+. Thus, substitution of Co2+ and Fe3+ together tunes the blue color of the cobalt compound to blue-green color arising from metal-to-metal charge transfer (MMCT) of Fe3+ and Co2+ ions. The tetrahedrally coordinated Ni2+ in the Dugganite imparts a magenta color.
1. INTRODUCTION Compounds stabilized in noncentrosymmetric structures are important for their symmetry dependent properties such as second-harmonic generation (SHG), ferroelectricity, multiferroics, and related behavior.1−6 Such solids find use in the areas of lasers, optical communications, computer memories, etc. Their properties and applications make it desirable to synthesize new compounds stabilized in noncentrosymmetric structures. There have been considerable efforts, both experimental as well as theoretical, to understand the formation of noncentrosymmetric compounds. The studies resulted in certain generalities, (a) cations that undergo second-order Jahn− Teller (SOJT) distortions, such as (i) high-valent d0 transition metal cations, (V5+, Nb5+, W6+, and Mo6+),7−11 and (ii) cations possessing a stereoactive lone pair of electrons (Pb2+, Bi3+, Se 4+ , Te4+ , I 5+ , etc.),12−16 (b) d 10 cations exhibiting considerable polar displacement in the center of the coordination environment (Zn2+, Cd2+, etc.),17−20 and (c) © 2019 American Chemical Society
anions having trigonal-planar geometry exhibiting asymmetric π-conjugated molecular orbitals (BO33−, NO3−, CO32−, etc.),21−26 that are likely to give noncentrosymmetric structures. Though these are general guidelines, the asymmetry of the local groups as mentioned above may align in a manner that leads to an overall centrosymmetric space group; accordingly, asymmetric local groups alone may not be a sufficient condition to realize macroscopic noncentrosymmetric structures. Therefore, it is a considerable challenge to design and prepare new compounds that stabilize in noncentrosymmetric space groups purely based on the above guidelines. In spite of these difficulties, many compounds have been stabilized in noncentrosymmetric space groups over the years.3,27 One such family of compounds is the Dugganite structure28 with the general formula [A3][B][C3][D2]O14, in Received: March 26, 2019 Published: June 21, 2019 8560
DOI: 10.1021/acs.inorgchem.9b00860 Inorg. Chem. 2019, 58, 8560−8569
Article
Inorganic Chemistry
spectrometer over the spectral region of 200−2500 nm. The reflectance data were converted to the Kubelka−Munk38 function by using the equation
which the A, B, C, and D cations having 8- (dodecahedron), 6(octahedron), and 4- (tetrahedron) coordinations, respectively. The presence of different coordination environments for the cations in the Dugganite structure has been exploited to produce interesting compounds.29−31 The presence of multiple coordination environments along with the noncentrosymmetric nature of the structure provides opportunities to explore many different properties. Thus, Dugganites exhibiting multiferroic behavior with antiferromagnetic ordering, such as Ba3NbFe3Si2O1432 Pb3TeCo3V2O14,33 and other nonlinear optical properties including SHG17 have been investigated. It would be interesting to learn about the role of SOJT effects from d0 cations in the Dugganite structure. There have been studies on the role of dn cations along with d0 cations for possible metal-to-metal charge transfer (MMCT) effects in solids.34 Dugganites provide opportunities to investigate such effects. We have been interested in exploring the Dugganite family (prototype mineral, Pb3TeZn3As2O14) due to the variable coordination preferences. Recently, we have investigated the garnet family, [A3][B2][C3]O12, another versatile and variable coordination structure, by careful substitution at the octahedral and tetrahedral sites.35 As a continuation of the theme, we have now explored the Dugganite structure mainly to expand the compositional variability by replacing the Te6+ ions with Sb5+ ions along with suitable substitutions at the tetrahedral sites. We have now successfully prepared and characterized new members of the Dugganite family, which are stabilized in the noncentrosymmetric space group P321 (no. 150). Besides the SHG property arising from noncentrosymmetric structure, we have explored the role of Pb2+(6s2) lone pair of electrons on the dielectric property, the role of V5+(d0) on SHG, and the role of multiple transition metal (dn) cations like Co2+, Ni2+, Cu2+, and Fe3+ etc. toward optical absorption and color to the compounds. The following compounds have been prepared: A3BC3D2O14 (A = Ba, Pb; B = Te, Sb; C = Al, Ga, Fe, Zn; D = Si, Ge, P, V). In this paper, we report the synthesis, structure, SHG, and other related studies of the new Dugganite members prepared by us.
F(R ) = (1 − R )2 /2R = α /S in which R is the reflectance, α is absorptivity, and S is the scattering factor. The optical band gaps were calculated from Tauc plots.39 The Tauc relation is αhν = A(hν − Eg )∧n where α is absorption coefficient, A is a constant called the band tailing parameter, and n is the power factor of the transition mode. Plot of (αhν)∧(1/n) versus the photon energy (hν) gives a straight line in a certain region. The extrapolation of this straight line intercepts the (hν)-axis to give the value of the optical band gap (Eg). NIR reflectance in the λ = 500−2500 nm range at room temperature were collected by using the same instrument. For characterization of pigment quality of the samples, the CIE 1931 chromaticity coordinates in the λ = 380−750 nm range were collected by using the same instrument. The CIE 1931 chromaticity coordinates were determined by using the gocie.exe program.40 SEM images and EDX data were recorded on a FEI ESEM Quanta 200 scanning electron microscope. Second-Order NLO Measurements. Powder SHG behavior was measured by using the Kurtz−Perry method with Q-switched Nd:YAG lasers at 1064 nm.6,41 The synthesized polycrystalline samples and the standard KDP, were ground and sieved into distinct particle size ranges (
