Recent progress in high pressure X-ray absorption spectroscopy studies at the ODE beamline
L. Nataf, F. Baudelet, A. Polian, I. Jonane, A. Anspoks, A. Kuzmin, T. Irifune
SSPECIAL ISSUE ”NANO-POLYCRYSTALLINE DIAMOND AND ITS AP-PLICATIONS”
Recent progress in high-pressure X-ray absorption spectroscopystudies at the ODE beamline
Lucie Nataf a , Fran¸cois Baudelet a , Alain Polian a , Inga Jonane b , Andris Anspoks b ,Alexei Kuzmin b and Tetsuo Irifune c a Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, Gif-sur-Yvette, France; b Instituteof Solid State Physics, University of Latvia, Riga, Latvia; c Geodynamics Research Center,Ehime University, Matsuyama, Ehime, Japan
ARTICLE HISTORY
Compiled February 25, 2020
ABSTRACT
High-pressure energy-dispersive X-ray absorption spectroscopy is a valuable struc-tural technique, especially, when combined with a nano-polycrystalline diamondanvil cell. Here we present recent results obtained using the dispersive setup of theODE beamline at SOLEIL synchrotron. The effect of pressure and temperature onthe X-ray induced photoreduction is discussed on the example of nanocrystallineCuO. The possibility to follow local environment changes during pressure-inducedphase transitions is demonstrated for α -MoO based on the reverse Monte Carlosimulations. KEYWORDS
High-pressure; nano-polycrystaline diamond anvil cell; XANES; EXAFS
1. Introduction
An alternative to the traditional pattern of beamlines dedicated to the X-ray ab-sorption spectroscopy, based on a two-crystal scanning mode, is given by the use ofdispersive optics [1–4]. In this technique, a bent crystal is used as a monochromator,and the setup is usually called Energy Dispersive EXAFS (EDE). The continuouschange of the Bragg incidence along the bent crystal opens an energy range in thereflected beam. The correlation between position and energy of the X-ray is exploitedthanks to a position sensitive detector. The setup can be used to acquire both theX-ray absorption near edge structure (XANES) as well as extended X-ray absorptionfine structure (EXAFS).The EDE beamline at SOLEIL synchrotron, called ODE for Optic DispersiveEXAFS [5], has extensively developed high-pressure XAS (X-ray Absorption Spec-troscopy) and XMCD (X-ray Magnetic Circular Dichroism) techniques. The XMCD
CONTACT Fran¸cois Baudelet. Email: [email protected] Address: SynchrotronSOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, FranceAlexei Kuzmin. Email: a.kuzmin@cfi.lu.lv Address: Institute of Solid State Physics, University of Latvia,Kengaraga street 8, LV-1063 Riga, Latvia a r X i v : . [ c ond - m a t . m t r l - s c i ] F e b ctivity was already presented in [6]. Here we report on some high-pressure measure-ments done with a nano-polycrystalline diamond anvil cell (NDAC) [7].The main advantages of dispersive XAS are the focusing optics, the short acquisi-tion time, and the great stability during the measurements due to the absence of anymechanical movement. This advantage allows the study of small samples, mandatoryin the case of high-pressure studies, where the sample chamber is a hole in a gasketsandwiched between two diamonds. The EDE technique is particularly adapted fordeglitching due to its live measuring process with classical diamonds, however, thereare some limits in the 10 keV range. The use of NDAC allows one to improve signifi-cantly the quality of the experimental signal eliminating spurious contributions fromthe diamond Bragg reflections [8]. This opens the route of many new possibilities asseen in the following contributions of XAS pressure measurements.
2. X-ray absorption spectroscopy at high-pressure
High-intensity X-ray beams at modern sources of synchrotron radiation can cause ra-diation damage to a material. The effect is well known in the case of metal-organiccomplexes [9–11]. This problem may be of particular importance for beamlines withthe energy-dispersive setup when a polychromatic X-ray beam with the spectral rangeof several hundred electron-volts is focused to the spot of several tens of microns on thesample located in the diamond anvil cell. In particular, when high-pressure measure-ments are performed, the indirect damage of the sample placed in a solution, whichplays the role of the pressure-transmitting medium, can occur due to the radiolysis ofthe latter. In the radiolysis process, reducing radicals such as solvated electrons andhydrogen atoms are produced upon X-ray irradiation of the solution and are responsi-ble for the sample change [12,13]. For example, the radiolysis can lead to a reductionof metal ions in aqueous solutions and is used for synthesis of metal nanoparticles[14–16].Recently, we have demonstrated X-ray induced photoreduction of nanocrystallineCuO, and its dependence on crystallite size, temperature and pressure [17]. Nanocrys-talline CuO (nano-CuO) powder samples with the average crystallite size of 8 nm and20 nm were prepared by a decomposition of Cu(OH) precipitate in air at 130 ◦ Cand 150 ◦ C, respectively. The Cu K-edge XANES spectra were collected in the pres-sure range of 0-23 GPa and the temperature range of 10-300 K. The sample pressureand temperature were controlled using a membrane-type nano-polycrystaline diamondanvil cell (NDAC) [7,8] and liquid helium cryostat. The use of NDAC allowed us toaccumulate the experimental data free from Bragg peaks due to the diamonds. Thepolychromatic photon flux on the sample was about 10 photons/s/eV in 25 × µ mFWHM.The sensitivity of the Cu K-edge XANES in nano-CuO (8 nm) to temperature andpressure is shown in Fig. 1(a). The emergence of metallic copper is visible at T =260 Kand P =2 GPa after 70 minutes of exposure to X-rays as an increasing shoulder at8983 eV and a decreasing main peak at 9000 eV. X-ray induced photoreduction oc-curs more rapidly at higher temperatures and lower pressure. For larger crystallitesize (20 nm), the reduction process takes longer time (Fig. 1(b)). At T =300 K and P =0.2 GPa, copper oxide is fully converted into metallic copper after about 90 minutesof irradiation. However, an increase of pressure to 23 GPa stabilizes the oxide phase.2 (cid:28)(cid:27)(cid:19) (cid:28)(cid:19)(cid:19)(cid:19) (cid:28)(cid:19)(cid:21)(cid:19) (cid:28)(cid:19)(cid:23)(cid:19) (cid:28)(cid:19)(cid:25)(cid:19)(cid:19)(cid:17)(cid:19)(cid:19)(cid:17)(cid:24)(cid:20)(cid:17)(cid:19)(cid:20)(cid:17)(cid:24)(cid:21)(cid:17)(cid:19)(cid:21)(cid:17)(cid:24) (cid:55)(cid:76)(cid:80)(cid:72)(cid:29) (cid:3)(cid:3)(cid:3) (cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:26)(cid:28)(cid:3)(cid:80)(cid:76)(cid:81) (cid:51)(cid:32)(cid:20)(cid:25)(cid:17)(cid:27)(cid:3)(cid:42)(cid:51)(cid:68)(cid:55)(cid:32)(cid:20)(cid:19)(cid:3)(cid:46)(cid:51)(cid:32)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68)(cid:55)(cid:32)(cid:21)(cid:25)(cid:19)(cid:3)(cid:46) (cid:3)(cid:3)(cid:3) (cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:26)(cid:19)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3)(cid:3)(cid:3) (cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:24)(cid:26)(cid:3)(cid:80)(cid:76)(cid:81) (cid:49) (cid:82) (cid:85) (cid:80) (cid:68) (cid:79)(cid:76) (cid:93) (cid:72) (cid:71) (cid:3) (cid:59) (cid:36)(cid:49) (cid:40)(cid:54) (cid:40)(cid:81)(cid:72)(cid:85)(cid:74)(cid:92)(cid:3)(cid:11)(cid:72)(cid:57)(cid:12) (cid:51)(cid:32)(cid:20)(cid:3)(cid:42)(cid:51)(cid:68)(cid:55)(cid:32)(cid:20)(cid:19)(cid:3)(cid:46) (cid:81)(cid:68)(cid:81)(cid:82)(cid:16)(cid:38)(cid:88)(cid:50)(cid:3)(cid:11)(cid:27)(cid:3)(cid:81)(cid:80)(cid:12)(cid:38)(cid:88)(cid:3)(cid:46)(cid:16)(cid:72)(cid:71)(cid:74)(cid:72) (cid:894)(cid:258)(cid:895) (cid:19)(cid:17)(cid:19)(cid:19)(cid:17)(cid:24)(cid:20)(cid:17)(cid:19) (cid:3) (cid:49) (cid:82) (cid:85) (cid:80) (cid:68) (cid:79)(cid:76) (cid:93) (cid:72) (cid:71) (cid:3) (cid:59) (cid:36)(cid:49) (cid:40)(cid:54) (cid:55)(cid:76)(cid:80)(cid:72)(cid:29) (cid:3)(cid:3) (cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:20)(cid:25)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:28)(cid:21)(cid:3)(cid:80)(cid:76)(cid:81)(cid:81)(cid:68)(cid:81)(cid:82)(cid:16)(cid:38)(cid:88)(cid:50)(cid:3)(cid:11)(cid:21)(cid:19)(cid:3)(cid:81)(cid:80)(cid:12) (cid:51)(cid:32)(cid:21)(cid:22)(cid:3)(cid:42)(cid:51)(cid:68)(cid:55)(cid:32)(cid:22)(cid:19)(cid:19)(cid:46) (cid:38)(cid:88)(cid:3)(cid:46)(cid:16)(cid:72)(cid:71)(cid:74)(cid:72) (cid:3) (cid:3) (cid:27)(cid:28)(cid:27)(cid:19) (cid:28)(cid:19)(cid:19)(cid:19) (cid:28)(cid:19)(cid:21)(cid:19) (cid:28)(cid:19)(cid:23)(cid:19) (cid:28)(cid:19)(cid:25)(cid:19)(cid:19)(cid:17)(cid:19)(cid:19)(cid:17)(cid:24)(cid:20)(cid:17)(cid:19) (cid:55)(cid:76)(cid:80)(cid:72)(cid:29) (cid:3)(cid:3)(cid:3) (cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:20)(cid:25)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:22)(cid:20)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:28)(cid:21)(cid:3)(cid:80)(cid:76)(cid:81) (cid:3) (cid:3) (cid:49) (cid:82) (cid:85) (cid:80) (cid:68) (cid:79)(cid:76) (cid:93) (cid:72) (cid:71) (cid:3) (cid:59) (cid:36)(cid:49) (cid:40)(cid:54) (cid:40)(cid:81)(cid:72)(cid:85)(cid:74)(cid:92)(cid:3)(cid:11)(cid:72)(cid:57)(cid:12) (cid:81)(cid:68)(cid:81)(cid:82)(cid:16)(cid:38)(cid:88)(cid:50)(cid:3)(cid:11)(cid:21)(cid:19)(cid:3)(cid:81)(cid:80)(cid:12) (cid:51)(cid:32)(cid:19)(cid:17)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68)(cid:55)(cid:32)(cid:22)(cid:19)(cid:19)(cid:46) (cid:38)(cid:88)(cid:3)(cid:46)(cid:16)(cid:72)(cid:71)(cid:74)(cid:72) (cid:894)(cid:271)(cid:895) Figure 1. (a) Temperature, pressure and time dependence of the Cu K-edge XANES of nano-CuO (8 nm).Solid line – starting spectrum, dashed line – spectrum after long time (57-79 min) exposition. Spectra are shiftedvertically for clarity. (b) Pressure and time dependence of the Cu K-edge XANES of nano-CuO (20 nm). Upperpanel – P=23 GPa, lower panel – P=0.2 GPa.
Note that the photoreduction was not observed for microcrystaline CuO at similarconditions. Thus, the rate of nano-CuO photoreduction to metallic copper increaseswith decreasing nanoparticle size but can be reduced by a decrease of temperatureor an increase of pressure. Performing experiment at low temperatures decreases themobility of reducing radicals [18,19], whereas an increase of pressure results in CuOnanoparticles agglomeration thus restricting their free surface and impeding reduction.The obtained results suggest that possible radiation damage should be taken into ac-count in experiments with high-flux X-ray beams, especially, in the case of nanosizedmaterials.
The sensitivity of EXAFS to the local atomic structure of a material and recent de-velopments in the EXAFS data analysis based on the reverse Monte Carlo (RMC)simulations [20] provide an invaluable tool to follow pressure-induced phase transi-tions. However, high-quality experimental data remain the main limiting factor tounleash the potential of the method.The pressure-induced (up to 36 GPa) transformations in 2D layered oxide α -MoO were studied at the Mo K-edge in [21]. Good quality experimental EXAFS data wereacquired using the NDAC cell and allowed us to perform analysis up to 6 ˚A using theRMC method. The structural models obtained by RMC give the Mo K-edge EXAFSspectra in good agreement with the experimental ones (Fig. 2). The correspondingatomic coordinates were used to calculate the radial distribution functions g ( R ) for3 (cid:22) (cid:23) (cid:24) (cid:25) (cid:26) (cid:27) (cid:28) (cid:20)(cid:19) (cid:20)(cid:20)(cid:16)(cid:22)(cid:16)(cid:21)(cid:16)(cid:20)(cid:19)(cid:20)(cid:21) (cid:3) (cid:40)(cid:91)(cid:83)(cid:72)(cid:85)(cid:76)(cid:80)(cid:72)(cid:81)(cid:87) (cid:3) (cid:53)(cid:48)(cid:38)(cid:3)(cid:73)(cid:76)(cid:87) (cid:68) (cid:16)(cid:48)(cid:82)(cid:50) (cid:22) (cid:83)(cid:32)(cid:19)(cid:17)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68) (cid:48)(cid:82)(cid:50) (cid:22) (cid:16)(cid:3)(cid:44)(cid:44)(cid:44) (cid:83)(cid:32)(cid:22)(cid:24)(cid:17)(cid:25)(cid:3)(cid:42)(cid:51)(cid:68) (cid:40)(cid:59) (cid:36) (cid:41) (cid:54) (cid:3) (cid:70) (cid:11) (cid:78) (cid:12) (cid:78) (cid:21) (cid:3) (cid:11) (cid:99) (cid:16) (cid:21) (cid:12) (cid:58)(cid:68)(cid:89)(cid:72)(cid:81)(cid:88)(cid:80)(cid:69)(cid:72)(cid:85)(cid:3)(cid:78)(cid:3)(cid:11)(cid:99) (cid:16)(cid:20) (cid:12) (cid:48)(cid:82)(cid:3)(cid:46)(cid:16)(cid:72)(cid:71)(cid:74)(cid:72) (cid:19) (cid:20) (cid:21) (cid:22) (cid:23) (cid:24) (cid:25)(cid:19)(cid:17)(cid:19)(cid:19)(cid:17)(cid:21)(cid:19)(cid:17)(cid:23)(cid:19)(cid:17)(cid:25)(cid:19)(cid:17)(cid:27) (cid:83)(cid:32)(cid:19)(cid:17)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68) (cid:48)(cid:82)(cid:50) (cid:22) (cid:16)(cid:3)(cid:44)(cid:44)(cid:44) (cid:48)(cid:82)(cid:3)(cid:46)(cid:16)(cid:72)(cid:71)(cid:74)(cid:72) (cid:41)(cid:55) (cid:3)(cid:3) (cid:48) (cid:50) (cid:39)(cid:56) (cid:47) (cid:56) (cid:54) (cid:3) (cid:11) (cid:99) (cid:16) (cid:22) (cid:12) (cid:39)(cid:76)(cid:86)(cid:87)(cid:68)(cid:81)(cid:70)(cid:72)(cid:3)(cid:53)(cid:3)(cid:11)(cid:99)(cid:12) (cid:3) (cid:40)(cid:91)(cid:83)(cid:72)(cid:85)(cid:76)(cid:80)(cid:72)(cid:81)(cid:87) (cid:3) (cid:53)(cid:48)(cid:38)(cid:3)(cid:73)(cid:76)(cid:87) (cid:68) (cid:16)(cid:48)(cid:82)(cid:50) (cid:22) (cid:83)(cid:32)(cid:22)(cid:24)(cid:17)(cid:25)(cid:3)(cid:42)(cid:51)(cid:68) (cid:20) (cid:21) (cid:22) (cid:23) (cid:24) (cid:25)(cid:19)(cid:24)(cid:20)(cid:19)(cid:20)(cid:24)(cid:21)(cid:19)(cid:21)(cid:24)(cid:22)(cid:19) (cid:48)(cid:82)(cid:16)(cid:50) (cid:53)(cid:39) (cid:41) (cid:3) (cid:74) (cid:11) (cid:53) (cid:12) (cid:3) (cid:11) (cid:68) (cid:87) (cid:82) (cid:80) (cid:86) (cid:18) (cid:99) (cid:12) (cid:39)(cid:76)(cid:86)(cid:87)(cid:68)(cid:81)(cid:70)(cid:72)(cid:3)(cid:53)(cid:3)(cid:11)(cid:99)(cid:12)(cid:3) (cid:3)(cid:22)(cid:24)(cid:17)(cid:25)(cid:3)(cid:42)(cid:51)(cid:68)(cid:3)(cid:19)(cid:17)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68) (cid:20) (cid:21) (cid:22) (cid:23) (cid:24) (cid:25)(cid:19)(cid:24)(cid:20)(cid:19)(cid:20)(cid:24) (cid:53)(cid:39) (cid:41) (cid:3) (cid:74) (cid:11) (cid:53) (cid:12) (cid:3) (cid:11) (cid:68) (cid:87) (cid:82) (cid:80) (cid:86) (cid:18) (cid:99) (cid:12) (cid:48)(cid:82)(cid:16)(cid:48)(cid:82) (cid:39)(cid:76)(cid:86)(cid:87)(cid:68)(cid:81)(cid:70)(cid:72)(cid:3)(cid:53)(cid:3)(cid:11)(cid:99)(cid:12)(cid:3) (cid:3)(cid:22)(cid:24)(cid:17)(cid:25)(cid:3)(cid:42)(cid:51)(cid:68)(cid:3)(cid:19)(cid:17)(cid:21)(cid:3)(cid:42)(cid:51)(cid:68) Figure 2.
Results of the RMC-EXAFS calculations for α -MoO (0.2 GPa) and MoO -III (35.6 GPa) phases.Upper row: comparison of the experimental and calculated Mo K-edge EXAFS spectra χ ( k ) k and their Fouriertransforms. Curves are shifted vertically for clarity. Lower row: the radial distribution functions (RDFs) forMo–O and Mo–Mo atom pairs reconstructed by the RMC method. Mo–O and Mo–Mo atom pairs as a function of pressure and allowed us to follow thedetails of local structure transformations upon phase transitions (Fig. 2).At room temperature, molybdenum trioxide exhibits two phase transitions uponcompression in the range of 0-43 GPa [22]. α -MoO transforms to monoclinic MoO -II phase ( P /m ) at ∼
12 GPa, and, next, to monoclinic MoO -III phase ( P /c )at ∼
25 GPa. The first two phases ( α -MoO and MoO -II) have layered structurecomposed of strongly distorted MoO octahedra, whereas a collapse of the interlayergap occurs in MoO -III phase [22].The difference between α -MoO and MoO -III phases is well established by EX-AFS. The transition is accompanied by a change of the Mo–O–Mo angles betweenneighbouring molybdenum-oxygen octahedra from ∼ ◦ and ∼ ◦ in α -MoO [23]to ∼ ◦ in MoO -III [22]. The disappearance of the Mo–O–Mo angle equal to 168 ◦ is responsible for a decrease of the second shell peak (at ∼ -III due to a reduction ofthe multiple-scattering (MS) effects within the Mo–O–Mo atomic chains.The reconstruction of the local environment around molybdenum using the reverseMonte Carlo (RMC) method [20] shed light on the pressure dependence of the radialdistribution functions (RDFs) for Mo–O and Mo–Mo atom pairs in details.At small pressure of about 0.2 GPa, there are three groups of two oxygen atomseach located at ∼ octahedrain α -MoO . At high pressure (35.6 GPa), the collapse of layered structure leads to anincrease of molybdenum coordination. Six nearest oxygen atoms from the same layer4re responsible for the peaks at ∼ ∼
3. Conclusion
In this paper, we describe the potential of high-pressure energy-dispersive X-ray ab-sorption spectroscopy (XANES/EXAFS) in combination with a nano-polycrystallinediamond anvil cell. The experimental setup is well suited for such measurements, mak-ing it possible to obtain experimental data of good quality, being free from the Braggcontribution from diamonds. At the same time, the accessible spectral range of thedispersive setup is restricted by the linear size of the detector, which imposes limita-tions on the resolution in real space. In addition, high intensity of X-rays focused ona sample can cause radiation damage.Two examples of high-pressure XAS studies of transition metal oxide compounds(CuO and MoO ) are discussed. They illustrate the sensitivity of copper oxide nanopar-ticles to reduction under X-ray irradiation and the ability to track local structuralchanges during phase transition in a 2D layered-type molybdenum trioxide using anadvanced analysis method based on the reverse Monte Carlo algorithm. Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
A.K. and I.J. are grateful to the Latvian Council of Science project no. lzp-2018/2-0353 for financial support. The research leading to these results has been partiallysupported by the project CALIPSOplus under the Grant Agreement No. 730872 fromthe EU Framework Programme for Research and Innovation HORIZON 2020.
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