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High-resolution Fourier TOF powder diffraction
Physica B 156 & 1.57 (1989) 567-570 North-Holland, Amsterdam
HIGH-RESOLUTION FOURIER TOF POWDER DIFFRACTION I. PERFORMANCE OF THE “MINI-SFINKS”
FACILITY
O.K. ANTSON’, A.P. BULKIN2, P.E. HIISM;iKI’, T.K. KOROTKOVA2, V.A. KUDRYASHEV’, H.S. KUKKONENl, V.G. MURATOV’, H.O. PijYRY’, A.F. SHCHEBETOV2, A.T. TIITTA’, V.A. TRUNOV* and V.A. UL’YANOV* ‘Technical Research Centre of Finland (VTT), Reactor Laboratory, Otakaari 3 A, SF-02150 Espoo, Finland ‘Leningrad Nuclear Physics Institute (LNPI), Academy of Sciences of the U.S.S.R., Gatchina, 188350 Leningrad district, USSR
A description of the Finnish-Soviet Fourier TOF neutron powder diffractrometer Mini-SFINKS is given. The facility has been used in its present configuration for a growing number of experiments since 1986. Some examples of these, including studies of high-T, superconductors, are given to illustrate the performance of the machine.
1. Introduction The high-resolution neutron powder diffractometer Mini-SFINKS [l, 21, which is the first practical result of a Finnish-Soviet cooperation aimed at the development of Fourier TOF techniques for diffractometry applications, has been operating at the 16 MW VVR-M reactor of the Leningrad Nuclear Physics Institute since 1984. In its present improved configuration described below the facility was completed in 1986 and it has since then been used quite routinely for an increasing variety of structural investigations. The successful operation of the Mini-SFINKS rests largely upon the use of the reverse time-offlight method of data acquisition which has been developed at the Technical Research Centre of Finland. This technique is particularly useful in Fourier TOF measurements as it provides an inherently on-line way of performing the required spectrum synthesis without any off-line data manipulations. Moreover, since the synthesis is obtained from the actual beam modulation frequencies given by the chopper, the possible systematic errors arising in the normal Fourier TOF method from inaccuracies in the chopper speed control are avoided. Still another advantage is that the chopper speed can be varied almost continuously, which besides making the
best use of measuring frame overlap problem.
time also removes
the
2. System description facility Fig. 1 shows the Mini-SFINKS schematically and table I summarizes some of its parameters for reference. The primary curved neutron guide of length 19.2 m gives a wellfiltered thermal beam which is led further to the sample area through a 4.8 m straight guide placed behind the chopper. These guides, both coated with 58Ni, provide an incident thermal
Fig. 1. Schematic diagram of the Mini-SFINKS diffractrometer: (1) Curved neutron guide, (2) straight guide section, (3) Fourier chopper, (4) optical pick-up, (5) sample, (6) scintillation glass neutron detector, (7) reverse time-of-flight analyzer, (8) SM-5 computer with disk and magnetic tape units, console, graphic terminal, printer and plotter. The scattering angle is 28 = 155” (nominal).
0921-4526/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
568
0. K. Antson
Table I Some parameters of the MiniSFINKS Standard sample size:
et al. I High-resolution
Fourier
TOFpowder
4 90 4.5
10.5 x 96.5 1.5 x 10’ 9 x lo-* 6.1 x 10” 155 7.615 0.5-2.6 0.95-5.1
flux of 1.5 x 107ncm-2s-’ over the -10 x 90 mm’ beam cross-section in the sample region. The 720-slit disk-type Fourier chopper, which uses a mixture of Gd,O, and epoxy resin as the neutron absorbing material, is run according to a suitable speed program from zero to a maximum speed of 10000 rpm to give a maximum beam modulation frequency of 120 kHz and thus a FWHM of = 8.5 ps for the chopper resolution function. With the other resolution components included, the total lattice spacing resolution changes in the useful measuring range from Ad/d = 0.5% at d = 0.5 8, to about 0.2% at d = 2 A as shown in fig. 2. The detector consists of four glass scintillator elements with a total area of 40 x 40 cm2. Each element is positioned and suitably inclined to approximate a time-focusing surface for Bragg scattering at about 1.2 m distance from the sample as shown in fig. 3. The rather large aperture of the detector system is sufficient to yield scattered neutron intensities exceeding 10’ n s-l with large samples (-4 cm3). Depending on the crystal structure of the specimen, good-quality TOF
sample ,’ detectors
Fig. 3. Scintillation glass detector system with the four timefocusing detector elements. The total detector area is 40 x 40 cm*.
diffractograms for profile refinement can then be measured usually in less than 24 hours. The diffraction patterns are accumulated by a reverse time-of-flight analyzer based on a special fast polarity correlator system performing the required Fourier synthesis. This is achieved by cross-correlating the detector intensity with differently delayed binary pickup sequences representing the neutron beam modulation. The synthetized TOF spectrum is simply the sum of these pickup sequences which are recorded neutron by neutron in an on-line fashion. The chopper speed can thus be varied nearly continuously during the measurement and hence the frame overlap effect causes no problems in practice. The specimens are normally enclosed in Ti-Zr zero-matrix containers and they can be measured in cryostats at temperatures between 4 K and room temperature or in furnaces operating from room temperature to 1300 K. In addition, high pressure chambers have been tested up to 15 kbar. 3. Experimental
’
’
0.L
’
1
0.8
’
’
1.2
I
facility.
radius (mm) height (mm) volume, V, (cm-‘)
Beam size at sample position (mm’) Flux at sample, cDs(ncm-’ SC’) Solid angle of detector, IV, (sr) Effective luminosity, Qs,W,V, Scattering angle, 20 (deg) Flight path, L (m) Effective measurement range: Lattice spacing (A) Neutron wavelength (A)
01 0
diffraction
’
1
1.6
’
’
2.0
’
1
2L
d/h
Fig. 2. Measured lattice spacing resolution as a function of d.
studies
Among the first experiments carried out with the Mini-SFINKS facility was the study of a possible connection between the structure and non-linear optical properties of some lanthanoid formates, e.g. Y(HCOO),. We could not confirm earlier X-ray results suggesting the existence
0. K. Antson et al. I High-resolution
of different structural modifications in these substances as the cause of their varying optical properties. The accurate refinement of hydrogen location in the formates confirmed, however, the existence of hydrogen bonding [3]. The investigations were later continued using also deuterated samples to study, e.g., the thermal vibration of the hydrogen atom more accurately [8]. Solid solutions of (Ce, La)B, were studied because of their promising properties as cold cathode materials and also because they show heavy fermion behaviour [4,7]. These investigations have been concentrated mainly on the possible existence of vacancies in the metal lattice and on the determination of the thermal parameters. More recently, an extensive series of experiments has been carried out on the high-temperature oxide superconductors. Specimens of both the La-Sr-Cu-0 and Y-Ba-Cu-0 systems have been synthetized and measured at different temperatures [5,6,9]. Our diffraction data of the La-Sr-Cu-0 system indicated anomalous structural behaviour in this interesting ceramic oxide. The high resolution of Mini-SFINKS was here a necessity in order to measure the temperaturedependent splitting of certain diffraction peaks and thus the structural transition temperature with good accuracy. In the superconducting Y-Ba-Cu-0 system we confirmed independently the fully ordered
I
1.5 Dhkl/A
L
20
Fig. 4. Measured diffraction pattern of YBa,Cu,O,_, superconductor. The lower curve is the residual error pattern after profile refinement.
Fourier TOF powder diffraction I
569
oxygen vacancy chains in the basal plane of the unit cell and also the strong anisotropy of the thermal vibrations of the oxygen atoms adjacent to the vacancy chains. These investigations have later been continued with Sr-doped specimens. Fig. 4 illustrates the quality of the diffraction data and the error curve obtained after the profile refinement in the case of YBa,Cu,O,_,. 4. Future prospects A project is already in progress to build a high-resolution reverse Fourier TOF diffractrometer using polarized neutrons at the new 100 MW PIK reactor now under construction at the LNPI. This second-generation machine is scheduled to start operation by the end of 1990. New developments are underway to reduce the effects of the often inadequately known background profile upon the quality of diffraction profile fits. This can be accomplished by filtering out the low-frequency components of the measured data as discussed in more detail in the second part of this paper [lo]. References [l] P. Hiismlki, V.A. Trunov, 0. Antson, V.A. Kudryashev, H. Kukkonen, H. Poyry, A.F. Shchebetov, A. Tiitta and VA. Ulyanov, Proc. Conf. on Neutron Scattering in the ‘Nineties’, Jiilich, 14-18 January, 1985 (IAEA, Vienna, 1985) p. 453. [2] V.A. Trunov, VA. Kudryashev, VA. Ulyanov, A.P. Bulkin, V.G. Muratov, T.K. Korotkova, A.F. Shchebetov, P. Hiismaki, H. Poyry, A. Tiitta, 0. Antson, H. Mutka and H. Kukkonen, Rep. No. 1277, Leningrad Nuclear Physics Institute (Leningrad, 1987), 60 pp. (in Russian). [3] V.A. Trunov, VA. Kudryashev, A.P. Bulkin, VA. Ulyanov, A.A. Loshmanov, N.G. Furmanova, 0. Antson, P. Hiismaki, H. Mutka, H. Poyry and A. Tiitta, Solid State Commun. 59 (1986) 95. [4] VA. Trunov, M.M. Korsukova, V.N. Gurin, VA. Kudryashev, VA. Ulyanov, 0. Antson, P. Hiismaki, H. Mutka, H. Piiyry and A. Tiitta, Sov. Phys. Solid State 29 (1987) 1883. [5] R.L. Bolotovsky, A.P. Bulkin, G.A. Krutov, VA. Kudryashev, S.V. Maleyev, B.P. Toperverg, V.A. Trunov, VA. Ulyanov, S.B. Vakhrushev, A.A. Loshmanov, O.K. Antson. P.E. Hiismiiki, H.O. Poyry, A.T. Tiitta and K.M. Ullakko, Rep. No. 1300, Leningrad Nuclear Physics Institute (Leningrad, 1987), 7 pp. (in Russian).
570
0. K. Antson
et al.
I High-resolution
[6] O.K. Antson, P.E. Hiismaki, H.O. Ptiyry, A.T. Tiitta, K.M. Ullakko, VA. Trunov and V.A. Ulyanov, Solid State Commun. 64 (1987) 757. (71 M.M. Korsukova, VN. Gurin, S.P. Nikanorov, V.A. Trunov, V.A. Kudryashev, VA. Ulyanov, 0. Antson, P. Hiismaki. H. Mutka, H. Pdyry, A. Tiitta, T. Lundstriim and L.-E. Tergenius, Rep. No. 1188, A.F. Ioffe Physico-Technical Institute (Leningrad, 1987), 18 pp. [8] VA. Kudryashev, G.A. Krutov, V.G. Muratov, V.A. Trunov. V.A. Ulyanov, 0. Antson, H. Kukkonen, H.
Fourier
TOFpowder
diffraction
1
Poyry. A. Tiitta, P. Hiismaki, A.A. Loshmanov and N.G. Furmanova, Sov. Phys. Solid State 29 (1987) 2174. [9] R.L. Bolotovsky, A.P. Bulkin, G.A. Krutov, V.A. Kudryashev, S.V. Maleyev, A.L. Malyshev, B.P. Toperverg, V.A. Trunov, V.A. Ulyanov, S.B. Vakhrushev, O.K. Antson, P.E. Hiismaki, H.O. Piiyry, A.T. Tiitta. K.M. Ullakko, M. Ahtee and M. Merisalo, Solid State Commun. 6.5 (1988) 1167. [ lo] P.E. Hiismaki, H.O. PGyry and J.I. Rantanen, these Proceedings, part II, Physica B 156 & 157 (1989) 571.
HIGH-RESOLUTION FOURIER TOF POWDER DIFFRACTION I. PERFORMANCE OF THE “MINI-SFINKS”
FACILITY
O.K. ANTSON’, A.P. BULKIN2, P.E. HIISM;iKI’, T.K. KOROTKOVA2, V.A. KUDRYASHEV’, H.S. KUKKONENl, V.G. MURATOV’, H.O. PijYRY’, A.F. SHCHEBETOV2, A.T. TIITTA’, V.A. TRUNOV* and V.A. UL’YANOV* ‘Technical Research Centre of Finland (VTT), Reactor Laboratory, Otakaari 3 A, SF-02150 Espoo, Finland ‘Leningrad Nuclear Physics Institute (LNPI), Academy of Sciences of the U.S.S.R., Gatchina, 188350 Leningrad district, USSR
A description of the Finnish-Soviet Fourier TOF neutron powder diffractrometer Mini-SFINKS is given. The facility has been used in its present configuration for a growing number of experiments since 1986. Some examples of these, including studies of high-T, superconductors, are given to illustrate the performance of the machine.
1. Introduction The high-resolution neutron powder diffractometer Mini-SFINKS [l, 21, which is the first practical result of a Finnish-Soviet cooperation aimed at the development of Fourier TOF techniques for diffractometry applications, has been operating at the 16 MW VVR-M reactor of the Leningrad Nuclear Physics Institute since 1984. In its present improved configuration described below the facility was completed in 1986 and it has since then been used quite routinely for an increasing variety of structural investigations. The successful operation of the Mini-SFINKS rests largely upon the use of the reverse time-offlight method of data acquisition which has been developed at the Technical Research Centre of Finland. This technique is particularly useful in Fourier TOF measurements as it provides an inherently on-line way of performing the required spectrum synthesis without any off-line data manipulations. Moreover, since the synthesis is obtained from the actual beam modulation frequencies given by the chopper, the possible systematic errors arising in the normal Fourier TOF method from inaccuracies in the chopper speed control are avoided. Still another advantage is that the chopper speed can be varied almost continuously, which besides making the
best use of measuring frame overlap problem.
time also removes
the
2. System description facility Fig. 1 shows the Mini-SFINKS schematically and table I summarizes some of its parameters for reference. The primary curved neutron guide of length 19.2 m gives a wellfiltered thermal beam which is led further to the sample area through a 4.8 m straight guide placed behind the chopper. These guides, both coated with 58Ni, provide an incident thermal
Fig. 1. Schematic diagram of the Mini-SFINKS diffractrometer: (1) Curved neutron guide, (2) straight guide section, (3) Fourier chopper, (4) optical pick-up, (5) sample, (6) scintillation glass neutron detector, (7) reverse time-of-flight analyzer, (8) SM-5 computer with disk and magnetic tape units, console, graphic terminal, printer and plotter. The scattering angle is 28 = 155” (nominal).
0921-4526/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
568
0. K. Antson
Table I Some parameters of the MiniSFINKS Standard sample size:
et al. I High-resolution
Fourier
TOFpowder
4 90 4.5
10.5 x 96.5 1.5 x 10’ 9 x lo-* 6.1 x 10” 155 7.615 0.5-2.6 0.95-5.1
flux of 1.5 x 107ncm-2s-’ over the -10 x 90 mm’ beam cross-section in the sample region. The 720-slit disk-type Fourier chopper, which uses a mixture of Gd,O, and epoxy resin as the neutron absorbing material, is run according to a suitable speed program from zero to a maximum speed of 10000 rpm to give a maximum beam modulation frequency of 120 kHz and thus a FWHM of = 8.5 ps for the chopper resolution function. With the other resolution components included, the total lattice spacing resolution changes in the useful measuring range from Ad/d = 0.5% at d = 0.5 8, to about 0.2% at d = 2 A as shown in fig. 2. The detector consists of four glass scintillator elements with a total area of 40 x 40 cm2. Each element is positioned and suitably inclined to approximate a time-focusing surface for Bragg scattering at about 1.2 m distance from the sample as shown in fig. 3. The rather large aperture of the detector system is sufficient to yield scattered neutron intensities exceeding 10’ n s-l with large samples (-4 cm3). Depending on the crystal structure of the specimen, good-quality TOF
sample ,’ detectors
Fig. 3. Scintillation glass detector system with the four timefocusing detector elements. The total detector area is 40 x 40 cm*.
diffractograms for profile refinement can then be measured usually in less than 24 hours. The diffraction patterns are accumulated by a reverse time-of-flight analyzer based on a special fast polarity correlator system performing the required Fourier synthesis. This is achieved by cross-correlating the detector intensity with differently delayed binary pickup sequences representing the neutron beam modulation. The synthetized TOF spectrum is simply the sum of these pickup sequences which are recorded neutron by neutron in an on-line fashion. The chopper speed can thus be varied nearly continuously during the measurement and hence the frame overlap effect causes no problems in practice. The specimens are normally enclosed in Ti-Zr zero-matrix containers and they can be measured in cryostats at temperatures between 4 K and room temperature or in furnaces operating from room temperature to 1300 K. In addition, high pressure chambers have been tested up to 15 kbar. 3. Experimental
’
’
0.L
’
1
0.8
’
’
1.2
I
facility.
radius (mm) height (mm) volume, V, (cm-‘)
Beam size at sample position (mm’) Flux at sample, cDs(ncm-’ SC’) Solid angle of detector, IV, (sr) Effective luminosity, Qs,W,V, Scattering angle, 20 (deg) Flight path, L (m) Effective measurement range: Lattice spacing (A) Neutron wavelength (A)
01 0
diffraction
’
1
1.6
’
’
2.0
’
1
2L
d/h
Fig. 2. Measured lattice spacing resolution as a function of d.
studies
Among the first experiments carried out with the Mini-SFINKS facility was the study of a possible connection between the structure and non-linear optical properties of some lanthanoid formates, e.g. Y(HCOO),. We could not confirm earlier X-ray results suggesting the existence
0. K. Antson et al. I High-resolution
of different structural modifications in these substances as the cause of their varying optical properties. The accurate refinement of hydrogen location in the formates confirmed, however, the existence of hydrogen bonding [3]. The investigations were later continued using also deuterated samples to study, e.g., the thermal vibration of the hydrogen atom more accurately [8]. Solid solutions of (Ce, La)B, were studied because of their promising properties as cold cathode materials and also because they show heavy fermion behaviour [4,7]. These investigations have been concentrated mainly on the possible existence of vacancies in the metal lattice and on the determination of the thermal parameters. More recently, an extensive series of experiments has been carried out on the high-temperature oxide superconductors. Specimens of both the La-Sr-Cu-0 and Y-Ba-Cu-0 systems have been synthetized and measured at different temperatures [5,6,9]. Our diffraction data of the La-Sr-Cu-0 system indicated anomalous structural behaviour in this interesting ceramic oxide. The high resolution of Mini-SFINKS was here a necessity in order to measure the temperaturedependent splitting of certain diffraction peaks and thus the structural transition temperature with good accuracy. In the superconducting Y-Ba-Cu-0 system we confirmed independently the fully ordered
I
1.5 Dhkl/A
L
20
Fig. 4. Measured diffraction pattern of YBa,Cu,O,_, superconductor. The lower curve is the residual error pattern after profile refinement.
Fourier TOF powder diffraction I
569
oxygen vacancy chains in the basal plane of the unit cell and also the strong anisotropy of the thermal vibrations of the oxygen atoms adjacent to the vacancy chains. These investigations have later been continued with Sr-doped specimens. Fig. 4 illustrates the quality of the diffraction data and the error curve obtained after the profile refinement in the case of YBa,Cu,O,_,. 4. Future prospects A project is already in progress to build a high-resolution reverse Fourier TOF diffractrometer using polarized neutrons at the new 100 MW PIK reactor now under construction at the LNPI. This second-generation machine is scheduled to start operation by the end of 1990. New developments are underway to reduce the effects of the often inadequately known background profile upon the quality of diffraction profile fits. This can be accomplished by filtering out the low-frequency components of the measured data as discussed in more detail in the second part of this paper [lo]. References [l] P. Hiismlki, V.A. Trunov, 0. Antson, V.A. Kudryashev, H. Kukkonen, H. Poyry, A.F. Shchebetov, A. Tiitta and VA. Ulyanov, Proc. Conf. on Neutron Scattering in the ‘Nineties’, Jiilich, 14-18 January, 1985 (IAEA, Vienna, 1985) p. 453. [2] V.A. Trunov, VA. Kudryashev, VA. Ulyanov, A.P. Bulkin, V.G. Muratov, T.K. Korotkova, A.F. Shchebetov, P. Hiismaki, H. Poyry, A. Tiitta, 0. Antson, H. Mutka and H. Kukkonen, Rep. No. 1277, Leningrad Nuclear Physics Institute (Leningrad, 1987), 60 pp. (in Russian). [3] V.A. Trunov, VA. Kudryashev, A.P. Bulkin, VA. Ulyanov, A.A. Loshmanov, N.G. Furmanova, 0. Antson, P. Hiismaki, H. Mutka, H. Poyry and A. Tiitta, Solid State Commun. 59 (1986) 95. [4] VA. Trunov, M.M. Korsukova, V.N. Gurin, VA. Kudryashev, VA. Ulyanov, 0. Antson, P. Hiismaki, H. Mutka, H. Piiyry and A. Tiitta, Sov. Phys. Solid State 29 (1987) 1883. [5] R.L. Bolotovsky, A.P. Bulkin, G.A. Krutov, VA. Kudryashev, S.V. Maleyev, B.P. Toperverg, V.A. Trunov, VA. Ulyanov, S.B. Vakhrushev, A.A. Loshmanov, O.K. Antson. P.E. Hiismiiki, H.O. Poyry, A.T. Tiitta and K.M. Ullakko, Rep. No. 1300, Leningrad Nuclear Physics Institute (Leningrad, 1987), 7 pp. (in Russian).
570
0. K. Antson
et al.
I High-resolution
[6] O.K. Antson, P.E. Hiismaki, H.O. Ptiyry, A.T. Tiitta, K.M. Ullakko, VA. Trunov and V.A. Ulyanov, Solid State Commun. 64 (1987) 757. (71 M.M. Korsukova, VN. Gurin, S.P. Nikanorov, V.A. Trunov, V.A. Kudryashev, VA. Ulyanov, 0. Antson, P. Hiismaki. H. Mutka, H. Pdyry, A. Tiitta, T. Lundstriim and L.-E. Tergenius, Rep. No. 1188, A.F. Ioffe Physico-Technical Institute (Leningrad, 1987), 18 pp. [8] VA. Kudryashev, G.A. Krutov, V.G. Muratov, V.A. Trunov. V.A. Ulyanov, 0. Antson, H. Kukkonen, H.
Fourier
TOFpowder
diffraction
1
Poyry. A. Tiitta, P. Hiismaki, A.A. Loshmanov and N.G. Furmanova, Sov. Phys. Solid State 29 (1987) 2174. [9] R.L. Bolotovsky, A.P. Bulkin, G.A. Krutov, V.A. Kudryashev, S.V. Maleyev, A.L. Malyshev, B.P. Toperverg, V.A. Trunov, V.A. Ulyanov, S.B. Vakhrushev, O.K. Antson, P.E. Hiismaki, H.O. Piiyry, A.T. Tiitta. K.M. Ullakko, M. Ahtee and M. Merisalo, Solid State Commun. 6.5 (1988) 1167. [ lo] P.E. Hiismaki, H.O. PGyry and J.I. Rantanen, these Proceedings, part II, Physica B 156 & 157 (1989) 571.