With 3.15: 1 molar ratio of MoO3 : K2MoO4 in a two-compartment porcelain electrolytic cell, blue crystals were formed at 550 C crystals of blue bronze gave room-temperature resistivities ofthe order of 1e-4 ohm-cm. the “blue” potassium molybdenum bronze K0.30MoO3. ESR spectra due to unpaired-electrons are observed. In this paper measurements of the K0.28M01.010J (blue). 3.5 MoO3: 1 K2MoO4 --> blue K0.28Mol.0lO3, Like the red bronze, the blue has layer structures the layers being composed of MoO6 octahedra sharing edges and corners The structure of the layers in the blue compound, the basic unit has ten octahedra (red has six). The co-ordination of the potassium atoms is also different. the blue phase is a metallic conductor above -100°C Hot potassium carbonate solutions will dissolve. sodium dihydrogen phosphate gentler for cleaning. Formed at 605—565 in gradient furnace. K0.33MoO3 is blue bronze.[WRONG] A blue-black bronze was formed at 550' and a red bronze was the product at 560'. From analytical data their formulas appear to be K0.28Mol.02O3 and K0.26Mo1.01O3, respectively A striking difference is ob- served. While the red potassium bronze K0.26- Mo1.0103 showed typical semiconduction behavior with a positive temperature dependency the blue-black bronze K0.28M01.0203 has a much lower resistivity with an apparent transition from semiconductor to metallic behavior above - 100'. This transition takes place over a broad temperature region The blue K0.28MoO3 is prepared by the electrolysis of fused salt mixtures of K2MoO4 and MoO3; it behaved as a metal. Slightly differing conditions gives red potassium bronze K0.26MoO3 a typical semi-conductor. Wold, Arnott, Kunnmann and Ferretti (1964). platty metallic blue crystals with perfect mica-like cleavage, secondary cleavage across flakes. Maximum elongation along b axis. Molybdenum atoms at y = 0, 1/4, 1/2. Two Mo ay 8(j) \pm(x,y,z) and \pm(x,\bar y,z). Unit cell contains 20 formula units. One potassium atom at a symmetry centre 2(d) (0,1/2,1/2). additional potassium atom in a fourfold site 4(i), \pm (x, 0, z) lying almost directly over one of the oxygen atoms in 8(j) there are no metal-to-metal bonds in the structure. Blue bronze has upper limit K0.3MoO3; red bornze is exactly K1/3MoO3. Potassium occupancy variable from 0.24 to 0.28. No evidence of ordering in the K vacancies K3Mo10O30 ideal blue bronze. K2Mo6O18 ideal red bronze There may be intergrowth of red and blue. K0.28MoO3 crystallizes in the monoclinic system, space groupl C2/m,with unit cell dimensions a=18.249, b=7.650, c = 9.855, beta = 117 deg 32 min ---------------------------------------------------------------------- Conductivity room temp 7e3 mho/cm Semiconductor-to-metal transiiton at 180 K Infinite sheets of Mo10O30 separated by layers of 3 K that hold the structure together. Each Mo10O30 has 3 electrons donated by K Ground state very weakly metallic Crystals of the blue bronze were obtained by electrolytic reduction of a Mo03:.Kz Mo04 melt in the mole ratio 3.35:1. 550 and 560'C to within 2'C over a period of several days. At the end of the electrolysis period, the crucibles were quickly dumped of their molten contents leaving the bronze behind. In ten trials, three of which were successful in yielding the blue bronze, the bronze was found at the bottom of the inner crucible, not on the electrode. Below 90'K the conductivity has a constant slope and then becomes weakly metallic below 10 K. The conductivity at 4.2 K is 6e-7 mho/cm At room temperature, 7e3 mho/cm ~ ---------------------------------------------------------------------- Careful control of growth conditions prevented mixture of red phase. crystals cleave by the separation of adjacent MO-O layers. the difference in resistivity for the two crystallographic directions studied is approximately 1 - l/2-2 orders of magnitude over the entire temperature range. transition from semiconducting to metallic behavior in samples oriented parallel to the b-axis. F SC-M transition seems to occur along the b axis. For these samples, the resistivity increases linearly as a function of temperature above approximately 180°K. Samples oriented perpendicular to the b-axis, however, exhibit a resistivity which is virtually constant at temperatures in excess of 180°K ---------------------------------------------------------------------- [Theoretical] The electronic structure of the blue bronze A0.30MoO3 (A = K, Rb) was examined ---------------------------------------------------------------------- Blue potassium molybdenum bronze, K0.28MoO3, was prepared by hydrothermal heating hydrogen molybdenum bronze in KCl solution at 431 K. Hydrated molybdenum bronze was found formed as an intermediate during the conversion from hydrogen molybdenum bronze to blue bronze. The hydrothermal method proved itself an easy and effective for synthesis of mixed-valence compounds. Manthiram et al. (12, 13) reported that, after a heat treatmentat 623-773 K of the amorphous products formed by the reduction of K2 MoO4 in KBH4 solution, K0.26MoO3, K0.30MoO3, and K0.85MoO3 were were crystallized with MoO2 . Single-phase blue potassium molybdenum bronze was prepared successfully at a temperature of 431 K by the hydrothermal synthesis route we used. I. A 1.296-g amountof HxMoO3 (ca. 0.009 mol), which can be prepared from MoO3 at ambient temperature following the previous procedure (19), was suspended in 30 ml of 0.9 M KCl solution in a Teflon-lined autoclave with a volume of 60 ml stirring on a magnetic stirrer, and then heated in a forced convection oven for certain specified times at 431 K and autogeneous pressure. HxMoO3 with various x values was used. Instead of single-phase HxMoO3, mixtures of HxMoO3 and MoO3 were also tested II. A 0.432-g amountof H0.28MoO3 (0.003 mol) was suspended in 30 ml of 0.9 M deaerated KCl solution in the Teflon-lined autoclave and stirred well with a glass rod. Different from route I, all the loading operations here were done in a nitrogen-fillled glove box. The autoclave was then heated in an oven for certain specified times at 431 K The resulting blue solid was separated by "ltration, ground to a "ne powder in a mortar, and then washed several times with distilled water using a centrifuge. ---------------------------------------------------------------------- The blue potassium bronze was obtained from the hydrated potassium molybdenum bronze in a nitrogen atmosphere at lower temperature by about 200 K than the usual fused method. The blue bronze is obtained directly in a solid phase. This is a new preparation method, compared with the usual method. R a m a n u j a c h a r y et" al.(7) also obtained a large crystal by heating starting m a t e r i a l s under the vacuum at 789-828 K. However, the authors obtained N a 0 . 9 M o 6 0 ~ 7 at 583 K from the h y d r a t e d sodium m o l y b d e n u m bronzes by neatlng in a n i t r o g e n a t m o s p h e r e ( 8 ) . The p r e p a r a t i o n t e m p e r a t u r e was lower by about 206-245 K than the usual fused methods. This method is very i n t e r e s t i n g because the reaction proceeds in a solid phase. The authors are trying to reveal this reaction m e c h a n i s m and want to apply to other solid phase reaction. In the series of these studies, the authors applied this new method for p r e p a r i n g the p o t a s s i u m m o l y b d e n u m bronze. The hydrated p o t a s s i u m m o l y b d e n u m bronze was used as the starting material and was heated in the n i t r o g e n atmosphere. We expected at first that K0.9 M o 6 0 1 7 type bronze could be o b t a i n e d as in the case of the sodium bronze, but, contrary to our e x p e c t a t i o n , the blue bronze of K 0.30MoO3 was obtained. This is a very i n t e r e s t i n g phenomenon. ---------------------------------------------------------------------- P.P. Tsai, J.A. Potenza, M. Greenblatt, H.J. Schugar(1986), "Crystal structure of {{chem|Li|0.33|MoO|3}}, a stoichiometric, triclinic, lithium molybdenum bronze". Journal of Solid State Chemistry, volume 64, issue 1, pages 47–56 {{doi|10.1016/0022-4596(86)90120-9}} A. Wold, W. Kunnmann, R. J. Arnott, and A. Ferreti (1964), "Preparation and properties of sodium and potassium molybdenum bronze crystals". Inorganic Chemistry, volume 3, issue 4, pages 545-547. {{doi|10.1021/ic50014a022}} J. Graham, N. C. Stephenson, A. D. Wadsley, and A. Wold (1965), "Potassium molybdenum oxide 'bronzes'" Nature, volume 206, pages 924-925 {{doi|10.1038/206924b0}} ---------------------------------------------------------------------- Acta Crystallographica Volume 20, Part 1 (January 1966) research papers Acta Cryst. (1966). 20, 93-100 [ doi:10.1107/S0365110X66000173 ] The crystal structure of the blue potassium molybdenum bronze, K0.28MoO3 J. Graham and A. D. Wadsley ---------------------------------------------------------------------- APS » Journals » Phys. Rev. B » Volume 6 » Issue 4 < Previous Article | Next Article > Phys. Rev. B 6, 1402–1412 (1972) Semiconductor-to-Metal Transition in the Blue Potassium Molybdenum Bronze, K0.30 MoO3; Example of a Possible Excitonic Insulator URL: http://link.aps.org/doi/10.1103/PhysRevB.6.1402 DOI: 10.1103/PhysRevB.6.1402 William Fogle and Jerome H. Perlstein ---------------------------------------------------------------------- Journal of Physics and Chemistry of Solids Volume 30, Issue 5, May 1969, Pages 1071–1076 Anisotropic electrical behavior of the blue potassium molybdenum bronze, K0·30MoO3 ☆ D.S. Perloff, M. Vlasse, A. Wold Departments of Physics and Chemistry and Division of Engineering, Brown University, Providence, R.I. 02912, U.S.A. http://dx.doi.org/10.1016/0022-3697(69)90362-X ---------------------------------------------------------------------- Band electronic structure of the molybdenum blue bronze A0.30MoO3 (A = K, Rb) First PageHi-Res PDF[783 KB]Citing Articles M. H. Whangbo , L. F. Schneemeyer Inorg. Chem., 1986, 25 (14), pp 2424–2429 DOI: 10.1021/ic00234a028 Publication Date: July 1986 ------------------------------------------------------------------------------ Kin Chin, Kazuo Eda, Noriyuki Sotani, M.Stanley Whittingham (2002), "Hydrothermal synthesis of the blue potassium molybdenum bronze, {{chem|K|0.28|MoO|3}}" Journal of Solid State Chemistry, volume 164, issue 1, pages 81–87. {{doi|10.1006/jssc.2001.9450}} ------------------------------------------------------------------------------ Materials Research Bulletin Volume 28, Issue 4, April 1993, Pages 363–368 Low temperature preparation of the blue potassium bronze from a hydrated potassium molybdenum bronze by heat treatment in a nitrogen atmosphere Noriyuki Sotani, Kazuo Eda Department of Chemistry, Faculty of Science, Kobe University, Tsurukabuto, Nada, Kobe 657, Japan Manabu Yanagi-ishi, Sadao Takagi Department of Chemistry, Faculty of Science and Technology, Kinki University, Kowakae, Higasi-Osaka 577, Japan http://dx.doi.org/10.1016/0025-5408(93)90069-P, How to Cite or Link Using DOI Permissions & Reprints ----------------------------------------------------------------------