摘要:

M. PASTERNAK 131 GENERAL DISCUSSION Prof. N. N. Greenwood (Newcastle upon Tyne) said It is always valuable when results obtained by one technique can be checked independently by another technique. Would Pasternak state how well the Mossbauer quadrupole results agree with the results obtained froni nuclear quadrupole resonance spectroscopy ; and are there any examples of gross discrepancies between the two techniques and what are the possible reasons for these? Dr. M. Cordey Hayes (Birmingham University) said N.q.r. data for SnI has shown resonances Corresponding to two inequivalent iodine sites. Did Pasternak observe two resonances in the 1291 Mossbauer data for this compound? Dr. M. Pasternak (Israel Atomic Energy Comm.) said In reply to Greenwood as far as I know there are no examples of gross discrepancies between the quadrupole coupling data derived from the M.E.in 1291 and those derived from N.Q.R. in compounds. Though recent experiments performed with 129SbI have shown a discrepancy of about 30 % as compared wih the N.Q.R. data those data are only preliminary and no conclusive statement can be drawn. In reply to Cordey Hayes nuclear quadrupole resonance results on SnI have shown two resonance lines with 3/1 intensity ratio corresponding to 1364 and 1384 Mc/sec quadrupole constants. Due to (i) the small difference in e2qQ which is almost equal to 2rexp. (= 17 Mc/sec) (ii) the 3/1 intensity ratio it was impossible to separate two distinct M.E. spectra. Dr. T. C. Gibb (University of Newcastle upon Tyne) said The observation by Pasternak of an enhanced intensity in the Am = 0 transitions would also be compatible with partial orientation in the source.Was this possibility eliminated and if so how ? Dr. M. Pasternak (Israel A. E. Commission Yavne) said In reply to Gibb the samples given in the paper regarding detection of anisotropic (x2> through the Goldanskii-Karyaguin effect were TeO and the group 4 tetra-iodides. In the first species an enhancement of Am = 0 transition was observed and this was related to an- isotropic <x2). Though in principle enhancement of the Am = 0 transition might be due to alignment of the principal e.f.g. axis perpendicular to the outgoing radiation this is not the case with TeO for the following reasons. (i) The TeO crystal is S . Bukshpan private communication. See ref. (20). 132 GENERAL DISCUSSION composed of chains similar to SeO,,’ and the coordination number of Te is three.The chain is helical and since the principal axis of the e.f.g. is perpendicular to the three oxygen plane its locus also forms a helix. Hence even with oriented crystals there is no preferred orientation of the principal e.f.g. axis. (ii) The samples were prepared from very fine powder mixed with polystyrene dissolved in benzene. This mode of preparation makes orientation highly improbable. Prof. R. H. Herber (Rutgers-The State University) said Since the information concerning the quadrupole splitting which one can get from an iodine 129 Mossbauer spectrum should be at least in principle identical to the information which one gets from an iodine 127n.q.r. experiment would Bukshpan comment on the extent of agreement or disagreement in the data that one gets from these two sets of experiments.In particular are there any instances in which the information which one gets from a Mossbauer spectrum is in serious disagreement with the information obtained from an N.Q.R. experiment ? Dr. S . Bukshpan (Israel A . E. Cornmission) said To the list presented by Pasternak in reply to Herber I would add a number of results obtained for iodine compounds e2qQ measured by M.E. in IiZ9 N.Q.R. results in compound in units of (Mc/sec) 1127 MC/W Sn14 -1364f15 1384 1394 Ge14 -15500f10 1500 1480 Si14 - 1335 f10 1324 1335 CI4 - 2102 f 10 21 30 CHSI - 1739f10 1765 CHI3 -2029f10 2046 As one can see the agreement is excellent. There is only one system Sb13 where we found a large discrepancy between the results of NQR and Mossbauer effect.In this compound we found a coupling e2qQ(11”) = 894Mc/sec and the reported value from NQR measurements is 1226 Mc/sec. We have made this experiment twice after careful preparation of the compound and each time with the same result. We do not have any explanation for this. Dr. J. A. Stone (du Punt de Nemours & Co. S. Carolina) said For the nuclear spin sequence 5/2 to 7/2 as in lz9I with pure quadrupole splitting and nonzero asymmetry parameter there are 12 possible transitions. The four additional “ forbidden ” transitions may be present due to admixing of the basis eigenfunctions. For 1291 would Pasternak indicate what would be the relative positions of the forbid- den transitions and have they ever been observed experimentally ? M. Pasternak (Israel A.E.Commission Yavne) said In reply to Stone the four additional “ forbidden ” transitions are the 5/24 112 ; 1 /2-+5/2 ; 1 /2-+7/2 and 3/24 7/2. Their positions and relative intensities for the three values of y are shown in table 1. W. Huckel StructuraE Chemistry of Inorganic Compounds (Elsevier Publishing Co. N.Y. 1951) p. 483. H. de Waard and C. B. van den Berg private communication. GENERAL DISCUSSION 133 For large q values the two transitions with relative significant intensities will be 1/2+ 5/2 and 3/2-+7/2. The first will be symmetric in position and equal in intensity with transition 1 (see table 3) at q = 1. The second will coincide with transition 8 and q = 1. Due to their small intensities those transitions have nevei been analyzed. TABLE 1 Energy positions in terms of e2qQg/4 and relative intensities (in parenthesis) for the additional " forbidden " transitions. The intensities normalization is the same as for the I C.G I given in table 3. AE'J 5/2+1/2 1/2+ 512 1 /2+ 712 3/2+7/2 0.1 1 *940 - 1.133 - 1 -990 - 1 -242 ( 7 . 5 ~ 10-3) (3.8 x lo-') (1 x 10-3) (2.3 x 10-3) 0-5 2.075 - 1.250 - 2.090 - 1-216 (5.6 x loM2) (0-62) (2x 10-2) (0-08) 0.9 2.280 - 1 496 - 2.280 - 1.065 (4.2 x lo-') (0.76) (5 x 10-2) (0.30)

ISSN:0430-0696    

DOI:10.1039/SF9670100131

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Mossbauer Spectroscopy of “Ni BY JON J. SPIJKERMAN National Bureau of Standards Washington D.C. 20234 Received 19th September 1967 The Mossbauer effect of 61Ni has been observed using a single line source prepared by 100 min LINAC irradiation. Of the many sources evaluated a 62NiCr (15 %) gave the best results with a frfactor of 0.1 and a linewidth of 0-097 cmlsec at 80°K. The source was activated by 100 MeV bremsstrahlung radiation using the 62Ni (y,p) 61Co reaction. The pulse height spectrum showed a single peak at 67-3 keV with no interfering radiation. The 1.7 h half-life of the source required repeated irradiations but annealing was not required. Several alloys and compounds of nickel were examined and showed partially resolved hyperfine interactions. The chemical shift is small for nickel compounds.The magnetic moment of the 5/2 spin 67.3 keV state is +0-425i-0443 nm measured from the magnetic hypefine interaction of a FeNi (1.5 %) alloy. Quadrupole splitting of the 5/2 state was observed in (NH4)6Wi~M~g032]. The application of Mossbauer spectroscopy in co-ordination chemistry has been clearly demonstrated for the study of co-ordination and metal organic compounds of iron and tin. It is of interest to extend this study to other elements particularly those of the fxst order transition series. The Mossbauer effect has been observed for 61Ni and 67Zn,1 but the source reported for 61Ni was magnetically split and the 67Zn Mossbauer linewidth is too narrow to be practical for chemical applications. 61Ni has suitable nuclear parameters for Mossbauer spectroscopy.The Mossbauer gamma radiation is 67.3 keV which is sufficiently penetrating to compensate for the 1.2 % normal abundance of the ground state. The spin of the excited state is 5/2 and 3/2 for the ground state which will make it possible to determine the sign of the electric field gradient (EFG). Furthermore it is of theoretical interest to compare the chemical shifts of nickel compounds with those of similar iron compounds. SOURCE PREPARATION The possible parent isotopes for 61Ni are 61Co and W u . The decays with 1-7 h half-life by p- to the 67.3 keV nickel excited state which is 100 % populated. 61Cu decays with a 3.3 h half-life by pf EC in a complex mode,2 4 % of which populates the 67.3 keV excited state. Both isotopes were produced by the NBS linear accelerator using a 1 h 100 MeV bremsstrahlung irradiation with the 63Cu (y,2n) 61Cu and 62Ni (y,p) 61Co reaction.The 61Co source gave an order-to-magnitude better signal/noise ratio. The half-lives of the radioisotopes are too short for radiochemical separations and source preparation. Since most elements are activated by photon reactions the choice of source matrix was limited to Al V and Cr which do not interfere. To obtain a cubic nonmagnetic and metallic environment for the 61Co nuclei the 62Ni was alloyed with 15 % Cr.3 The pulse height spectrum of this source obtained with a 0.25 cm thick NaI(T1) scintillation detector is shown in fig. 1 and the MiSssbauer spectrum using a 2 % 61Ni-Cu alloy absorber in fig. 2. The linewidth of this source absorber system is 0~110+0~002 cm/sec at 80°K. Corrected for thickness broadening the width is 0.097 or 20 % wider than 0-076 cmlsec natural width.Annealing the source after irradiation did not decrease the observed linewidth. This would correspond to a residual 134 FIG. 1 .-Pulse height spectrum of the 100 MeV Brei?ir\ttdi/iriz.q irradiated "Ni -C'r (15 "i) MijssbaLier soLircc. [ 7b f;lCC' JXlgC I 34. J . J . SPIJKERMAN 135 internal magnetic field of 15 kilogauss at the Ni site. have shown by the nuclear magnetic resonance spin-echo technique that the hyperfine field at the Ni site in the NiCr system has a major contribution from the Ni magnetic Streever and Uriano PO2 I.01 - - 1-00 c.I ." U 3 .r( f 0-99 6) .-.I U 3 2 0-98 097 li I lb O-I50cm/s 0 20 40 60 80 100 120 140 160 180 channel number FIG. 2.-Mossbauer spectrum of the Ni-Cr (1 5 %) source and a 2 % NiCu absorber at 80°K.OD FIG. 3.-Debye-Waller factorfas a function of the Debye temperature for 61Ni recoil free resonant absorption at 4 and 80°K. moment and a small contribution from the magnetic moments of the neighbouring Cr atoms. The addition of 15 % Cr to nickel depressed the Curie temperature well below 80"K but increasing the Cr concentration to 17 % did not decrease the observed Mossbauer linewidth. 136 MOSSBAUER SPECTROSCOPY OF 61Ni The source has a f-factor of 0-10f0*01* at 80"K determined by zero velocity resonant absorption? using a 15 % NiCr alloy for both the source and absorber. This agrees well with the 420°K Debye temperature for nickel metal as shown in fig. 3. MAGNETIC HYPERFINE INTERACTIONS The magnetic hyperfine spectrum of 61Ni consists of 12 transitions from a 5/2 spin excited to a 3/2 spin ground state shown in fig.4. The ground-state magnetic dipole moment of 0.7487 nm has been measured by a n.m.r. technique.' To deter- mine the moment of the excited state the Mossbauer spectrum of a 1.5 % 61Ni-Fe t t t / / T '4f t * 4 0 FIG. $.-Energy level diagram for the magnetic hyperfine interaction of the (5/2) and (3/2) 61Ni spin states showing the intensities of the allowed (MI) transitions. 10 alloy was obtained as shown in fig. 5. Analysis of this spectrum gave a moment for the excited state of +0.425+0.043* nm and an internal magnetic field of 241 k7 kilogauss at the nickel site. This field agrees well with the n.m.r. value of 235 kilogauss obtained by Streever et aL8 Fig. 6 shows the spectrum of anti-ferromagnetic NiO 9* lo at 80°K.The internal magnetic field corresponds to 96f 10 kilogauss. Although the magnetic hyperfine spectra are not resolved with computer techniques it is possible to measure internal magnetic fields of nickel compounds or alloys with a random error of 10 % (relative standard deviation of the average) for fields larger than 20 kilogauss. CHEMICAL SHIFT IN Ni COMPOUNDS The range of chemical shifts observed for nickel compounds is much smaller than for iron. However measurements of the chemical shifts of several nickel compounds listed in table 1 indicate that useful information can be obtained. To * error is standard deviation of the average. J . J . SPlJKERMAN 137 TABLE I.-M6SSBAUER PARAMETERS FOR NICKEL COMPOUNDS AND ALLOYS AT 80°K. 62NiCr (1 5 %) SOURCE absorber Ni CuNi(2 %) CuNi (20 %) FeNi (1.5 %) NiF2 K2NiF4 NiO (NH4)61NiNMo90321 6lNi content rnglcmz 5 8.2 3.4 10 0.7 7.2 - chemical shift cm/sec + 0.002 f0.002 - 0.003 f0-001 - 0.010 f0*003 +0.010 f0.001 + 0.0126 f0-0040 + 0.01 3 f0.005 + 0.005 f0.002 - 0.033 f0.008 % effect 6.2 h0.5 3-8 f0.4 4.0 f0.5 7.3 f0-3 3.7 f0.3 4.8 f0.4 14.1 k0.5 3.2 f0.4 NBS source nickel-chromium (15 %) absorber iron-nickel (1 -5 %) 1.010 1.005 h too0 Y .* .t a $ .g 0995 2 s 0990 e .- + 0.985 0.980 1 0 1 ! I 1 1 0 20 40 60 80 100 120 140 160 180 200 channel number FIG. 5.-Mossbauer spectrum of a 1-5 % NiFe alloy absorber at 80°K. NI3S spectrum run no. absorber NiO 1'010 1- J O C 5 '990 .C( 0 .zi '980 2 2 '370 .d * .3 * 960 * 950 0 0.150 1 CM/Scc. I I I ' 220 3Wl T 9 740 4 0 3;il JI 1 3:u 3Bo 'lW channel number FIG.6.-M&sbauer spectrum of antiferromagnetic NiO at 80°K. 138 MOSSBAUER SPECTROSCOPY OF 61Ni interpret these shifts a chemical shift-electron configuration diagram similar to that presented for iron by Walker Wertheim and Jaccarino," is shown in fig. 7. The free-ion Hartree-Fock calculations of Watson l2 were used to obtain the total s-electron density at the nucleus for the various 3d configurations of the nickel free ion and the Fermi-Segre-Goudsmit formula was used to calculate the 4s electron I I I 1 I 20 40 6 0 80 I Q O 120 X= %4s electron contribution FIG. 7.Tentative chemical shift-electron configuration diagram for nickel. The chemical shift is calibrated with the s-electron density and 4s contribution for the nickel 3d configurations. C = 14905 ai3.density contribution from the optical spectra l3 of nickel to establish the slope of the configurations on the diagram. The diagram is calibrated using the chemical shifts of Ni with a 3d9 4soq6 14* l5 and NiFz with a 3d8 4s0 configuration. The diagram shows that the chemical shift decreases with increasing electron density indicating that the charge radius of the excited state is smaller than that for the ground state. AR/R is thus negative as for 57Fe. is derived. The largest chemical shift was observed for (NH4)6[NiMo9032],16 where nickel has a formal oxidation state of +4.17 The complex ion has D3 symmetry. The Ni (IV) ion resides in a trigonally-distorted octahedron of oxide atoms. The strong field octahedral environment for the Ni ion would give a d6 configuration which is supported by the magnetic susceptibility measurement of Ms = 0.065 magnetons.18 This configuration is also indicated by the diagram of fig.7. The spectrum of (green) NiO is confusing. This compound is antiferromagnetic and has a cubic structure at 273"K but has a tetragonal distortion below 90°K. This can account for the asymmetry in the spectrum. From the preliminary calibration a value of AR/R = 2.5 x QUADRUPOLE SPLITTING From the known spin states of the Mossbauer transition the quadrupole split spectrum should consist of 5 lines. However the n.m.r. work of Locher and J . J . SPIJKERMAN 139 Geschwind l9 rules out the possibility of observing the ground state (3/2) quadrupole splitting in 61Ni by Mossbauer spectroscopy and only the excited state splitting can be observed as is shown in fig.8. From the X-ray data the trigonal distortion in this Ni4+ complex is large. The triplet separation can be used to determine the source nickel-chromium(l5 %) absorber [NiM0,0~~1 I I I I channel number FIG. 8.-Mossbauer spectrum of (NH4)6[NiIVMoo032] at 80°K. sign of the EFG once the sign of the quadrupole moment Qe has been established. To observe a larger splitting spectra were taken of several planar nickel compounds but the Mossbauer effect was not observed at 80°K. Further studies at lower temperatures are planned to determine the sign and magnitude of Qe. CONCLUSION The work described is a preliminary study of Ni Mossbauer spectroscopy. At present the source preparation requires a linear accelerator or betatron but Coulomb excitation can also be used.As more nickel Mossbauer data becomes available the source can be improved in f-factor and linewidth which will increase the resolution. With the present source much information can be obtained on nickel- bearing magnetic materials. The applications in chemistry are many particularly since the quadrupole spectra will also provide the sign of the EFG. The interpretation of the chemical shift in Ni compounds is far from complete. Much data and correlations with molecular orbital calculations will be required to use this parameter in structural determinations. The Mossbauer sources were irradiated by the Radiation Physics Division of NBS. Without the assistance of Dr. D. K. Snediker in preparing the many alloys of enriched nickel isotopes this work would not have been completed. Several spectra were computer analyzed by J.C. Love of ORNL. The author thanks Dr. B. W. Dale of Georgetown University for the preparation of the ammonium 9- molybdo-nickelate (IV). The helpful discussions with Dr. J. R. DeVoe of NBS Dr. L. May of Catholic University and Dr. M. T. Pope and Dr. B. W. Dale of George- town University are gratefully acknowledged. A. H. Muir K. J. Ando and H. M. Coogan M3ssbauer Data Index 1958-1965 (John Wiley and Sons New York N.Y. 1966) p. 107 and 178. H. H. Bolotin and H. J. Fishbeck Physic. Rev. 1967 158 1069. M. Hansen Constitution ofBinary Alloys (McGraw-Hill New York N.Y. 1958) p. 542. 140 MOSSBAUER SPECTROSCOPY OF 61Ni R. L. Streever and G. A. Uriano Physic. Rev. 1966 149,295. J. A. Ragne and W. R. G. Kemp Phil. Mag. 1956 1,918. R. D. Lawson M.H. MacFairlane and T. T. S. Kuo Physics Letters 1966,22,168. R. L. Streever L. H. Bennett R. C. LaForce and C. F. Day J. Appl. Physics 1963,34,1050. Y. Shimomura M. Kojima and S. Saito J . Physic. SOC. Japan. 1956,11 1136. lo S. Yamaguchi 2. physik. Chem. 1963 222 78. l1 L. R. Walker G. K. Wertheim and V. Jaccarino Physic. Rev. Letters 1961 6,98. l2 R. E. Watson Physic. Reu. 1960,119,1934 ; Technical Report no. 12 (Solid-state and Molecular Theory Group MIT June 15,959). l3 C. E. Moore Atomic Energy Levels NBS Circ. no. 467 (U.S. Gov. Printing Office Washington D.C. 1952) vol. 2 pp. 99-103. NiV has not been reported. l4 C. Kittel Introduction to Solid State Physics (John Wiley New York N.Y. 1956). l5 J. W. D. Connolly Physic. Rev. 1967 159 415. l6 This compound was synthesized using 10 % enriched 61Ni by B. W. Dale. l7 L. C. W. Baker and T. J. R. Weakley J. Znorg. Nucl. Chem. 1966,28,447. l9 P. R. Locher and S . Geschwind Physic. Rev. Letters 1963 11 333. ' L. E. Drain Physics Letters 1964 11 114. P. Ray A. Bhaduri and B. Sarma J. Indian Chem. Soc. 1948,25 51.

ISSN:0430-0696    

DOI:10.1039/SF9670100134

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

140 MOSSBAUER SPECTROSCOPY OF 61Ni AUTHOR INDEX* * The references in heavy type indicate papers submitted for discussion. Bancroft G. M. 48 85 115. Bryukhanov V. A. 69. Bukshpan S. 132. Clark M. G. 19,49 101. Clear M. 13. Cordey Hayes M. 66 101 131. Danon J. 11 12 47 68 83. Davies D. W. 66. Duncan J. F. 13 15 47 64 65 83 99 103 115 116 118. Freeman A. G. 49. Gallagher P. K. 40 48 49 101. Gibb T. C. 99 117 131. Gol'danskii V. I. 59. Greenwood N. N. 15 20 29 39 47 48 51 Gutlich P. 84 97. Herber R. H. 19 86 97 98 99 100 101 132. Iofa B. Z. 69. Johnson C. E. 7 12 14 15 30. Kothekar V. 69. van der Kraan A. M. 38. 75 83 99 116 131. Krishnan R. 39 50. van Loef J. J. 38. Lyubutin I. S. 31. MacChesney J. B. 40. MacKede K. J. D. 103. Makarov E. F. 31 59. Parish R. V. 13 20 75. Pasternak M. 119 131 132. Perkins P. G. 51 65. 66 67 68. Pillinger W. L. 77. Povitskii V. A. 31. Semenov S. I. 69. Shpinel V. S. 69 75. Simopoulos A. 15. Spijkerman J. J. 134. Stewart D. J. 103 Stone A. J. 65. Stone J. A. 77 82 84 85 132. Trotter K. 13. Trozzolo A. M. 26. Wall D. H. 51. Wickman H. H. 21 29 30.

ISSN:0430-0696    

DOI:10.1039/SF9670100140

出版商:RSC    

年代:1967

数据来源: RSC