Characterization of MnO 4 ' / KBr Single Crystal

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Lenard Ira Shelton
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1 MM Jour. Myan. Acad. Arts & S& 2005 Vol. m. No. 3(i) Physics Characterization of MnO 4 ' / KBr Single Crystal Win Kyaw, Win Zaw, Thein Soe, Pho Kaung and Sein Htoon Abstract Manually operated X-ray diffractometer (Tel-X-Gmeter 580) was upgraded successfully into the Personal Computer (PC) based instrument. Utilizing this together with Fourier Transform Infrared (FTIR) Spectrophotometer investigates the effect of doping Permanganate, MnO 4 ', ions into Potassium Bromide, KBr, single crystal. XRD spectra of the pure KBr single crystal and the MnO 4 * doped KBr ( MnO 4 " / KBr ) single crystal are found to be similar irrespective of the dopant MnQ 4 " ion. The IR spectrum, however, confirms the existence of MnO 4 " matrix isolated in KBr, The high intensity of the resonance Rmasn transitions is employed to examine the dopants in substrate which are present in such low abundances that conventional Raman Spectroscopy cannot detect. Key words: XRD, Interfacing PC, Tel-X-Omster, MnO 4 " / KBr Single Crystal, FTIR Introduction MnCV ion has been subjected to several spectroseopie studies both in solutions and in different crystalline environments. The choice of this particular system is based on many criteria. Single crystals of KBr doped with M11O4" ion can easily be grown in a laboratory. The crystals are stable under normal conditions and can be handled without any special care. The host matrix KBr which is often used as an IR window for Infrared Spectra, does not absorb in the spectral domain of MnOV ion. Unlike the other T<j molecules, there is little Fermi resonance interference/ 1 x * 2> 3 ' 4> 5) ) The pure KMn >4 crystal has needle shape, dark purple colour and orthorhombic crystal system. T he pure KBr crystal has cubic shape, white and cubic crystal system. The orientation of the MnCV / KBr crystals is straightforward since they also grow in the form of cubes with natural (100) faces. The Mn(V ion o f KMnC>4 substitutes for Br ~ anion o f KBr without changing the macroscopic cubic shape and the microscopic cubic structure. In other words, MnCV ion is isolated in KBr crystal. XRD study examines whether MnO 4 " /.KBr crystals retain the original cubic structure while FTIR study confirms the existence of M21O4" matrix isolated in KBr crystals. The Department of physics, Yangon University

2 26 Jour. Myan. Acad. Arts & Sc Vol. III. No. 3(i) Physics? high intensity of the resonance Raman transitions can also be used to find the very diluted MnCV dopant present in KBr. Experiment Single crystals of KBr doped with Mn(V have been grown by slow evaporation of aqueous solutions. Laboratory grade KBr and KMJ1O4 powders were used. The solution contains typically 0.5% by weight of KM11O4 with respect to KBr. Transparent and homogeneously pink colored crystals were selected for the measurements. A complete computer interface for the Tel-X-Ometer should consist of (a) a means of acquiring a count rate from a detector, ( b ) a means of recording the angular position of the detector arm, ( c ) a mechanism by which the computer can increment the angular position of the detector arm and/ or crystal mount between readings ( if possible for a particular system ), and ( d ) software instructions to plot the data so that peak position may be obtained. The block diagram showing the interface is given in Fig 1. Error! Tel-X-Ometer(580) X-rays Computer Stepper Motor Control Program Fig 1 Experimental setup

3 Jour. Myan. AcatL Arts & Sc 2005 Vol. m. No. 3(i) Physics 27 The conditioning circuit is constructed for counting pulses input from a G M tube. The output of the conditioning circuit then presents, for each input pulse, a digital pulse to the digital input of the PC's Line Printer Terminal (LPT), A stepper motor is mounted in a bracket attached to the thumbwheel on the detector arm; its shaft is then mechanically coupled to the end of a shaft that is installed coaxially with the thumbwheel. As the thumbwheel and the stepper motor shafts are rotated step by step through the digital outputs of LPT, the detector arm is taken through a Bragg angle 9. The software was developed in C++ programming language. XRD Study Results and Discussion The structures of pure KBr and MnCV / KBr single crystals were characterized by the PC-based X-ray Bragg-speetrometer (Tel-X-Ometer 580) using Cuka radiation (wavelength of A with 20 kv/ 80 JLI A), sampling width of 0.2, and scan speed of 5 / min, in the 20 range of GM counter with the working voltage of 420 V is used as a radiation detector. The PC-based Tel-X-Ometer records the position and relative intensities of the various reflected lines. All reflections of the FCC lattice are present in the XRD spectrum of KBr crystal (See Fig 2). All the peak heights and peak positions are in good agreement with JCPDS (Joint Committee on Powder Diffraction Standards) file data for KBr. The XRD spectrum of MnO4" / KBr crystal is given in Fig 3. It shows a similar nature as that of KBr confirming that the FCC structure is retained. Vlforational Study The IR spectrum was recorded in the middle wave number range of cm" 1 by means of FTIR'spectrometer (FTER Shimadzu). The resolution was 4cm" 1 and the number of scans was fixed to 60. The IR spectrum of MnO4" / KBr crystal at room temperature is shown in Fig 4. It shows a single sharp absorption line at 924 cm" 1. The four normal modes expected in a tetrahedral MnO4~ molecule transforms as Ai, E, 2Fz respectively. Inspection o ft he t etrahedral T d sy mmetry s hows that only t he modes transforming as F2 are IR and Raman active. The line at 924 cm" 1 transforms as F2 since it was observed in both FTIR and Raman spectra/ 7 )

4 28 Jour. Myan. Acad. Arts & Sc Vol. III. No. 3(i) Physics. This fact assures the existence of M11O4" in KBr. The Raman spectrum of MnCV in KBr single crystal is shown in Fig 5. The line at 927 cm" 1 confirms with the F2 of FTIR spectrum. From the structural and vibrational analysis, the structure of MnCV /KBr crystal is conjectured to be FCC with substitution of MnCV ion in Br" anion (See Fig 6). Jenway 6300 is a microprocessor controlled Visible Range Spectrophotometer covering the wavelength range of 320 to 1000 nm with a 10 nm bandwidth. Fig 7 shows the first electronic band of charge transfer character of MnCV lines around 510 nm i t I O o A Theta( degree ) Fig 2 XRD pattern of KBr single crystal

5 Jour. Myan. Acad. Arts & Sc Vol. III. No. 3(i) Physics o I <N Fig 3 XRD pattern of MnO 4 7 KBr single crystal 2-Theta(degree ) Wave number (cm-1) Fig 4 The infrared spectrum of KBr doped with MnO 4 ' single crystal at room temperature

6 30 Jour. My an, Acad. Arts & Sc Vol. III. No. 3(i) Physfcs i cm 1 Raman shift (cm' 1 ) Fig 5 The Raman spectrum of MnO 4 " /KBr single crystal at room temperature [001J O &y MB o [010] [100] Fig 6 Crystal Structure of MnO 4 7 KBr

7 Jour. Myan. Acad. Arts & Sc Vol. m. No. 3(i) Physics g " \ he wavelength (nm) Fig 7 Absorption spectrum MnO 4 " /KBr single crystal

8 32 Jour. Myan. Acad. Arts & Sc Vol. III. No. 3(i) Physics (a) Fig 8 A schematic representation of a charge transfer transition in which an electron initially on the outer atoms (represented by the grey tint in a) migrate to the central ion 848 2X848 3X t)0 l 500 i i i l l i l l i l l t Fig 9 The resonant Raman spectra of MnO 4 " in KBr Wave number (cm-1)

9 Jour. Myan. Acad. Arts & Sc Vol. III. No. 3(i) Physics. 33 The first electronic band of charge transfer character of MnG 4 " lines around 510 nm (see Fig 7). The absorption of a photon can often be traced to the excitation of electrons that Ipelong to a small group of atoms. For sample, when a carboiiyl group is present an absorption at about 290 run is normally observed. Groups with characteristic optical absorptions are called chrornophores ( from the Greek for 'colour bringer 5 },. and their presence often accounts for the colours of substances. A d-meta! complex may absorb light as a result of the transfer of an electron from the ligands into the d-orbital of the central atom, or vice-versa ( Fig 8 ). In such charge transfer transitions the.electron moves through, a considerable distance, which means that the redistribution of charge may be large and the absorption correspond permanganate ion Mn(V ; the charge redistribution that accompanies the migration of an electron from the O atoms to the central Mn atom accounts for its intense violet colour (resulting from absorption in the range 420 to 700nm).Thus the Raman intensities of the very diluted MnCV are greatly enhanced through.a resonant Raman effect when one uses the visible exciting lines of the diode laser (520 nm). The resonant Raman spectra of MnCV in KBr (Fig 9) reveals two intense bond progressions, namely 848, 2 x 848, 3 x 848, etc., , x 848 cm" 1, etc. In resonance Raman spectra, it is common to observe harmonic progressions of the totally symmetric mode. Itis a pleasure to thank IWATANINAOGI foundation, 10-2, 2- chome, Nagatacho, Chiyoda - ku, Tokyo , Japan through the good offices of Dr Thi Tin Lay of Nanomaterials Lab. Japan for a gift of SHIMADZU FTIR-8400 Fourier Transform Infrared Spectrophotometer.

LAB 01 X-RAY EMISSION & ABSORPTION

LAB 01 X-RAY EMISSION & ABSORPTION LAB 0 X-RAY EMISSION & ABSORPTION REPORT BY: TEAM MEMBER NAME: Ashley Tsai LAB SECTION No. 05 GROUP 2 EXPERIMENT DATE: Feb., 204 SUBMISSION DATE: Feb. 8, 204 Page of 3 ABSTRACT The goal of this experiment