Davoli, Ivan

Dingwell, Donald B.

Mottana, Annibale

Paris, Eleonora

Seifert, Friedrich

English

Open Access LMU

Condensed Matter and Materials Communications Volume 1 Number 2, pp. 115-121,1993 ISSN 1067-6147 © 1993 Nova Science Publishers, Inc. A HIGH-TEMPERATURE DEVICE FOR IN SITU MEASUREMENT OF X-RAY ABSORPTION SPECTRA Friedrich Seifert Bayerisches Geoinstitut, Universität Bayreuth, D-8580 Bayreuth (Germany) Eleonore Paris Universita1 di Camerino, Dip. Scienze della Terra, 1-62032 Camerino (Italy) Donald B. Dingwell Bayerisches Geoinstitut, Universität Bayreuth, D-8580 Bayreuth (Germany) Ivan Da voli Universita' di Camerino, Dip. Matcmatica e Fisica, 1-62032 Camerino (Italy) Annibale Mottana Universita1 di Roma "La Sapienza", Dip. Scienze della Terra, 1-00185 Roma (Italy) (Received on 14 December, 1992 by A. Marcelli) Abstract Description of a high temperature cell designed to record the X-ray absorption spectra of samples heated in situ up to 1500 °C under the vacuum (10~4 torr) of a synchrotron X-ray beam line. Application to determination of the transition (at ca. 220 °C) from incommensurately-modulated to normal structure in Ca2Co[Si207l melilite and the coordination of Ti on K20-Ti02-Si02-melts. PACS. No. 07.20.Hy, 78 J0.Dm, 64.70.Dv Introduction X-ray absorption (XAS) spectra yield sensitive information on site geometry, valence, and long-range as well as short-range ordering of atoms in crystalline and amorphous compounds. For a characterization of materials undergoing unquenchable phase transitions, or for following the kinetics of a phase change or reaction, measurements under in situ conditions at elevated temperatures are essential. Moreover, geologically as well as technologically-significant transitions from the solid to the liquid state that cannot be studied by the conventional X-ray diffraction techniques can be studied continuously by X-ray absorption spectroscopy, provided a suitable in situ high-temperature cell (HTC) is available. 115 116 F. Seifert et al. We present here the design and first applications of a HTC especially conceived for XAS which has been tested successfully for both XANES and EXAFS measurements at the PULS X-ray line of the synchrotron radiation facility of Frascati. Design requirements A high-temperature cell to be used for XAS spectroscopy has to fulfill the following technical requirements: - homogeneous temperature distribution; - negligible heating of surrounding parts such as windows, vacuum seals, etc.; - remote control of sample position; - operation in vacuum; - good transparency to X-rays in the pertaining energy region; • sample holders that minimize the problem of contamination and/or X-ray absorption, but maximize heat transfer; - accomodation of several samples, or of samples with different thicknesses. Experimental setup To achieve these goals, a furnace such as that depicted in Fig. 1 has been constructed. The entire furnace assembly is mounted to a ISO mm vacuum flange containing the feed-throughs for cooling water, heating power (rated to 10 A maximum), and thermocouple, and is then inserted into the experimental vacuum chamber of the X-ray beam üne. Vertical movements of the assembly relative to the vacuum chamber are made possible by a motor-driven stainless-steel bellows. cooling jacket Figure 1: Cross-section through the 800 °C furnace. The symbol S designates the sample compartment, Ni the nickel heating block, BN the boron nitride plates, ruling to the left the stainless-steel caps and jackets, ruling to the right the brass frame of the celL Right: detail of the nickel block that serves as sample holder. Samples are placed into the five rectangular slits. A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 117 Depending on the temperature range and/or number of samples required, three different designs for the heating element and sample holder have been developed. They all fit the same furnace shell surrounded by water-cooled jacket, and can easily be exchanged. For the temperature range up to about 800 °C stainless-steel tube is used onto which an Inconel-coated, MgO-insulated heating wire (rated to 1000 °Q is firmly wound and fixed. The interior sample-holder consists of a central nickel block (Ni) sandwiched by sintered boron nitride plates (BN) and steel end-caps. The outer two boron nitride layers serve for the heat transfer to die nickel block and to the samples (S). Temperatures are measured and controlled by a sheared NiCr/Ni thermocouple placed inside the nickel block. Typical power consumption at 800 °C in a 10^ torr vacuum is about 500 W. End plates of the furnace with slits 100 mm wide χ 40 mm high (corresponding to the total sample area) prevent excessive thermal radiation to the outside of the furnace. The central nickel block (Fig. 1, right) contains five slits (3 mm high χ 10 mm wide χ 4 mm thick) which serve as sample compartments. In the high-energy application (e.g. for the study of Fe or Co K-edges) the appropriate amount of sample (several mg, depending on the type and concentration of the element studied) are intimately mixed with about 50 mg of boron nitride powder to ensure a homogeneous thickness, pressed into the slits of the nickel block, and covered on both sides by thin (1 mm) sheets of boron nitride to hold the sample in place. In the low-energy region (e.g. for studying the Ti K-edge), or if reaction with boron nitride might become a problem, the samples are mounted on a fine metal mesh grids (see below) and attached to the nickel block without the sintered boron nitride cover sheets. In the temperature ranges up to 1200 °C and 1500 °C Kanthai A l and a Pt90RhlO (d=0.35 mm, 5 m long) heating wire, respectively is wound directly onto a AI2O3 ceramic tube (do=25 mm, dj =20 mm) and fixed by Z1O2 cement. A radiation shield of Pt foil between the heating tube and the water-jacket minimize thermal losses. Maximum current is 8 A and power consumption is 850 W at 1500 °C. The sample holder, made out of BN or AI2Q3 machinable ceramic, can accomodate two 3 χ 10 mm samples. For these high-temperature applications, the finely powdered samples are pressed into a metal mesh grid (stainless steel, tantalum, or platinum). Even rather fluid melts were found to be held in place on the vertically mounted mesh just by surface tension. This arrangement gives minimal intensity losses (ca. 20%) and contamination. In the high-temperature set up, temperature controlled is achieved by a Pt90Rhl0 thermocouple and ramped (maximum 1500 °C /h) Eurotherm controller operating in phase angle firing mode and power control. Typical temperature stability over extended periods of time (hours) is 1 °C. Phase transition in melilite The 800 °C cell has been used for a study of the phase transition in synthetic Ca2Co[Si207] melilite by Co K-edge XANES and EXAFS spectroscopy. The high-T structure of this melilite consists of 4-fold coordinated C0O4 polyhedra linked with S12O7 dimers to form a sheetlike arrangement. Ca atoms occupy the 8-fold coordinated sites between the sheets. It is well known from TEM, Mössbauer, X-ray diffraction, NMR, and DTA studies [1] that many melilite-type compounds, and the Ca2Co[Si207] phase in particular, undergo a non-quenchable, hysteresis-free phase transition from the high-temperature normal phase to a low-temperature, incommensurately modulated phase in which the S12O7 dimers are rotated and kinked and the C0O4 tetrahedra deformed [2]. For Ca2Co[Si207], the phase transition temperature is at 210-200 °C [1]. As the phase transition is approached from lower temperatures, the structure changes by a decrease in modulation amplitude and increases in modulation wavelength in the direction towards the high-T normal structure, but nevertheless the final phase transition is sharp and of the lambda type. Local fluctuations of the structure might persist to temperatures above the phase transition. As to be expected for a phase transition in which only subtle changes of the structure occur (e.g. no change in coordination number or valence, but only changes in angular and 118 F. Seifert et al. Figure 2: Normalized Co K-edge XANES spectra of Ca2Co[Si207] melilite taken at room temperature (top) and at 261°C (middle), and their difference spectrum (bottom). A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 119 bond-length distortion), the changes in XANES and EXAFS spectra as a function of temperature are only slight. Fig. 2 gives the normalized 261 °C Co K- XANES spectrum (i.e. above the phase transition, in the field of the normal melilite structure) and the room-temperature spectrum (in the stability field of the modulated phase). 0 100 200 300 400 Temperature (°C) Figure 3: Energy positions of the Co K-edge peak b (bottom) and of the peak d (above) of melilite Ca2Co[Si207] as a function of temperature. The vertical bars indicate the experimental uncertainty in energy. Temperature uncertainty is less than the width of the plotted square. Energy changes of the XANES features are related to changes in the structural environment around the absorbing atom [3]. In Ca2Co[Si2Ö7] melilite, first attempts to evaluate the peak positions (Fig. 3) indicate minor but rather systematic trends for the strong first peak (b) and the weaker second peak (d), but no changes for the pre-edge peak (a), and just weak changes for the third peak (c). For both peaks b and d, the energy reaches minima close to the phase transition, near 220 °G For a final assessment, the recording of the spectra with higher energy resolution and the fitting of the spectral envelope to sums of Lorentzians will be required. However, the trends observed so far can tentatively be referred to the anomalous thermal expansion of the structure near the phase transition [4]. T1O2 coordination in silicate melts and glasses T1O2 is a crucial component of terrestrial and lunar magmas, high temperature slags and modern melt-based ceramic materials. The growth of high-purity T1O2 crystals from the melts is also of industrial importance. The concentration of T1O2 in natural melts ranges up to 16% and ceramic materials can even be richer in T1O2. Thus, the effects of this major component on transport properties as well as its partial molar properties are important input for the modeling on crystal-melt interaction. The coordination of Ti4+ in silicate glasses has been little investigated to date, but the existing data point to features which can be interpreted as a mixture 4, 5, and 6-coordinated T i 4 + . Among the clearest distinctions between, for example, 4- and 6-coordination is the 120 F. Seifert et al. presence of a strong pre-peak for the 4-fold coordination as opposed to a weaker one for the 6-fold coordination [5]. XAS studies on quenched silicate glasses [6] indicate the presence of either 4-, 5- or 6-coordinated Ti 4 ^, or a mixture of 4- and 6-fold coordination. These results suggest that Ti coordination is very sensitive to chemical or physical parameters and that, at a given composition, Ή might behave differendy in a melt compared to a glass. The XANES spectrum of a melt of ^S i jT iOi i composition, obtained at 1300 °C following heat treatment in the HTC at temperatures up to 1450 °C is compared with the room temperature of the glass in Fig. 4. The broad features of the spectra are similar but details differ. The relative intensity of the pre-peak remains high in the high-temperature liquids, consistent with the coordination number intermediate between 4 and 6 for Ίι 4* in the liquid as in the glass. These examples testify the broad application field of in-situ high-temperature XAS analysis. Expecially regarding the study of melts, of geological as well as technological relevance, this device will allow to obtain structural information not suitable to be obtained by other methods. 4955 4978 5002 5026 5050 Energy (eV) Figure 4: XANES spectra of a K2Si4TiOn composition as quenched glass at room temperature (top) and as liquid at 1300 °C. (bottom). A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 121 Acknowledgements Financial support was given by P.S. CNJfc. "Metodi cristallografici avanzati", by Bayerisches Geoinstitut, Deutsche Forschungsgemeinschaft and Fonds der chemischen Industrie. Setup of die cell and first experiments were carried out by F.S. while being on sabbatical leave from University of Bayreuth to that of Rome. We all thank the staff of PULS, Frascati, for their cooperation and S. Priori (Frascati), R. Weigel and G. Herrmansdörfer (Bayreuth) for technical support References [1] F. Röthlisberger, F. Seifert, and M. Czank. Eur. J. Mineral., 2,585-594 (1990). [2] C Van Heurck, G. Van Tendeloo, and S. Amelinckx. Phys. Chem. Minerals, 18,441-452 (1992). [3] A. Bianconi. In "EXAFS and Near Edge Structure" (Eds. A. Bianconi, L. Incoccia and S. Stipcich). Springer, Berlin, 118-129 (1983). [4] S. L. Webb, C R. Ross Π, and J. liebertz. Phys. Chem. Mineral 18,522-525 (1992). [5] A. Mottana, E. Paris, G. Delia Ventura, and J.-L. Robert Rend. Uncei Sc. Fis. 9,1, 387-392(1990). [6] T. Dumas, and J. Petiau. / . Non-Cryst. Solids, 81,201-220 (1986). 

In &quot;EXAFS and Near Edge Structure&quot; (Eds.

A high-temperature device for in situ measurement of X-ray adsorption spectra

Universität München: Elektronischen Publikationen

Condensed Matter and Materials Communications 
Volume 1 Number 2, pp. 115-121,1993 
ISSN 1067-6147 
© 1993 Nova Science Publishers, Inc. 
A HIGH-TEMPERATURE DEVICE FOR IN SITU MEASUREMENT 
OF X-RAY ABSORPTION SPECTRA 
Friedrich Seifert 
Bayerisches Geoinstitut, Universität Bayreuth, D-8580 Bayreuth (Germany) 
Eleonore Paris 
Universita1 di Camerino, Dip. Scienze della Terra, 1-62032 Camerino (Italy) 
Donald B. Dingwell 
Bayerisches Geoinstitut, Universität Bayreuth, D-8580 Bayreuth (Germany) 
Ivan Da voli 
Universita' di Camerino, Dip. Matcmatica e Fisica, 1-62032 Camerino (Italy) 
Annibale Mottana 
Universita1 di Roma "La Sapienza", Dip. Scienze della Terra, 1-00185 Roma (Italy) 
(Received on 14 December, 1992 by A. Marcelli) 
Abstract 
Description of a high temperature cell designed to record the X-ray absorption spectra of 
samples heated in situ up to 1500 °C under the vacuum (10~4 torr) of a synchrotron X-
ray beam line. Application to determination of the transition (at ca. 220 °C) from 
incommensurately-modulated to normal structure in Ca2Co[Si207l melilite and the 
coordination of Ti on K20-Ti02-Si02-melts. 
PACS. No. 07.20.Hy, 78 J0.Dm, 64.70.Dv 
Introduction 
X-ray absorption (XAS) spectra yield sensitive information on site geometry, valence, 
and long-range as well as short-range ordering of atoms in crystalline and amorphous 
compounds. 
For a characterization of materials undergoing unquenchable phase transitions, or for 
following the kinetics of a phase change or reaction, measurements under in situ conditions at 
elevated temperatures are essential. Moreover, geologically as well as technologically-
significant transitions from the solid to the liquid state that cannot be studied by the 
conventional X-ray diffraction techniques can be studied continuously by X-ray absorption 
spectroscopy, provided a suitable in situ high-temperature cell (HTC) is available. 
115 
116 F. Seifert et al. 
We present here the design and first applications of a HTC especially conceived for 
XAS which has been tested successfully for both XANES and EXAFS measurements at the 
PULS X-ray line of the synchrotron radiation facility of Frascati. 
Design requirements 
A high-temperature cell to be used for XAS spectroscopy has to fulfill the following technical 
requirements: 
- homogeneous temperature distribution; 
- negligible heating of surrounding parts such as windows, vacuum seals, etc.; 
- remote control of sample position; 
- operation in vacuum; 
- good transparency to X-rays in the pertaining energy region; 
• sample holders that minimize the problem of contamination and/or X-ray absorption, but 
maximize heat transfer; 
- accomodation of several samples, or of samples with different thicknesses. 
Experimental setup 
To achieve these goals, a furnace such as that depicted in Fig. 1 has been constructed. The 
entire furnace assembly is mounted to a ISO mm vacuum flange containing the feed-throughs 
for cooling water, heating power (rated to 10 A maximum), and thermocouple, and is then 
inserted into the experimental vacuum chamber of the X-ray beam üne. Vertical movements of 
the assembly relative to the vacuum chamber are made possible by a motor-driven stainless-
steel bellows. 
cooling jacket 
Figure 1: Cross-section through the 800 °C furnace. The symbol S designates the sample 
compartment, Ni the nickel heating block, BN the boron nitride plates, ruling to the left the 
stainless-steel caps and jackets, ruling to the right the brass frame of the celL Right: detail of 
the nickel block that serves as sample holder. Samples are placed into the five rectangular slits. 
A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 117 
Depending on the temperature range and/or number of samples required, three different 
designs for the heating element and sample holder have been developed. They all fit the same 
furnace shell surrounded by water-cooled jacket, and can easily be exchanged. 
For the temperature range up to about 800 °C stainless-steel tube is used onto which an 
Inconel-coated, MgO-insulated heating wire (rated to 1000 °Q is firmly wound and fixed. The 
interior sample-holder consists of a central nickel block (Ni) sandwiched by sintered boron 
nitride plates (BN) and steel end-caps. The outer two boron nitride layers serve for the heat 
transfer to die nickel block and to the samples (S). Temperatures are measured and controlled 
by a sheared NiCr/Ni thermocouple placed inside the nickel block. Typical power consumption 
at 800 °C in a 10^ torr vacuum is about 500 W. End plates of the furnace with slits 100 mm 
wide χ 40 mm high (corresponding to the total sample area) prevent excessive thermal 
radiation to the outside of the furnace. 
The central nickel block (Fig. 1, right) contains five slits (3 mm high χ 10 mm wide χ 4 
mm thick) which serve as sample compartments. In the high-energy application (e.g. for the 
study of Fe or Co K-edges) the appropriate amount of sample (several mg, depending on the 
type and concentration of the element studied) are intimately mixed with about 50 mg of boron 
nitride powder to ensure a homogeneous thickness, pressed into the slits of the nickel block, 
and covered on both sides by thin (1 mm) sheets of boron nitride to hold the sample in place. In 
the low-energy region (e.g. for studying the Ti K-edge), or if reaction with boron nitride might 
become a problem, the samples are mounted on a fine metal mesh grids (see below) and 
attached to the nickel block without the sintered boron nitride cover sheets. 
In the temperature ranges up to 1200 °C and 1500 °C Kanthai A l and a Pt90RhlO 
(d=0.35 mm, 5 m long) heating wire, respectively is wound directly onto a AI2O3 ceramic tube 
(do=25 mm, dj =20 mm) and fixed by Z1O2 cement. A radiation shield of Pt foil between the 
heating tube and the water-jacket minimize thermal losses. Maximum current is 8 A and power 
consumption is 850 W at 1500 °C. The sample holder, made out of BN or AI2Q3 machinable 
ceramic, can accomodate two 3 χ 10 mm samples. For these high-temperature applications, the 
finely powdered samples are pressed into a metal mesh grid (stainless steel, tantalum, or 
platinum). Even rather fluid melts were found to be held in place on the vertically mounted 
mesh just by surface tension. This arrangement gives minimal intensity losses (ca. 20%) and 
contamination. 
In the high-temperature set up, temperature controlled is achieved by a Pt90Rhl0 
thermocouple and ramped (maximum 1500 °C /h) Eurotherm controller operating in phase 
angle firing mode and power control. Typical temperature stability over extended periods of 
time (hours) is 1 °C. 
Phase transition in melilite 
The 800 °C cell has been used for a study of the phase transition in synthetic Ca2Co[Si207] 
melilite by Co K-edge XANES and EXAFS spectroscopy. The high-T structure of this melilite 
consists of 4-fold coordinated C0O4 polyhedra linked with S12O7 dimers to form a sheetlike 
arrangement. Ca atoms occupy the 8-fold coordinated sites between the sheets. It is well known 
from TEM, Mössbauer, X-ray diffraction, NMR, and DTA studies [1] that many melilite-type 
compounds, and the Ca2Co[Si207] phase in particular, undergo a non-quenchable, hysteresis-
free phase transition from the high-temperature normal phase to a low-temperature, 
incommensurately modulated phase in which the S12O7 dimers are rotated and kinked and the 
C0O4 tetrahedra deformed [2]. For Ca2Co[Si207], the phase transition temperature is at 210-200 
°C [1]. As the phase transition is approached from lower temperatures, the structure changes by 
a decrease in modulation amplitude and increases in modulation wavelength in the direction 
towards the high-T normal structure, but nevertheless the final phase transition is sharp and of 
the lambda type. Local fluctuations of the structure might persist to temperatures above the 
phase transition. 
As to be expected for a phase transition in which only subtle changes of the structure 
occur (e.g. no change in coordination number or valence, but only changes in angular and 
118 F. Seifert et al. 
Figure 2: Normalized Co K-edge XANES spectra of Ca2Co[Si207] melilite taken at room 
temperature (top) and at 261°C (middle), and their difference spectrum (bottom). 
A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 119 
bond-length distortion), the changes in XANES and EXAFS spectra as a function of 
temperature are only slight. Fig. 2 gives the normalized 261 °C Co K- XANES spectrum (i.e. 
above the phase transition, in the field of the normal melilite structure) and the room-
temperature spectrum (in the stability field of the modulated phase). 
0 100 200 300 400 
Temperature (°C) 
Figure 3: Energy positions of the Co K-edge peak b (bottom) and of the peak d (above) of 
melilite Ca2Co[Si207] as a function of temperature. The vertical bars indicate the experimental 
uncertainty in energy. Temperature uncertainty is less than the width of the plotted square. 
Energy changes of the XANES features are related to changes in the structural 
environment around the absorbing atom [3]. In Ca2Co[Si2Ö7] melilite, first attempts to evaluate 
the peak positions (Fig. 3) indicate minor but rather systematic trends for the strong first peak 
(b) and the weaker second peak (d), but no changes for the pre-edge peak (a), and just weak 
changes for the third peak (c). For both peaks b and d, the energy reaches minima close to the 
phase transition, near 220 °G 
For a final assessment, the recording of the spectra with higher energy resolution and 
the fitting of the spectral envelope to sums of Lorentzians will be required. However, the trends 
observed so far can tentatively be referred to the anomalous thermal expansion of the structure 
near the phase transition [4]. 
T1O2 coordination in silicate melts and glasses 
T1O2 is a crucial component of terrestrial and lunar magmas, high temperature slags and 
modern melt-based ceramic materials. The growth of high-purity T1O2 crystals from the melts 
is also of industrial importance. The concentration of T1O2 in natural melts ranges up to 16% 
and ceramic materials can even be richer in T1O2. Thus, the effects of this major component on 
transport properties as well as its partial molar properties are important input for the modeling 
on crystal-melt interaction. 
The coordination of Ti4+ in silicate glasses has been little investigated to date, but the 
existing data point to features which can be interpreted as a mixture 4, 5, and 6-coordinated 
T i 4 + . Among the clearest distinctions between, for example, 4- and 6-coordination is the 
120 F. Seifert et al. 
presence of a strong pre-peak for the 4-fold coordination as opposed to a weaker one for the 6-
fold coordination [5]. XAS studies on quenched silicate glasses [6] indicate the presence of 
either 4-, 5- or 6-coordinated Ti 4 ^, or a mixture of 4- and 6-fold coordination. These results 
suggest that Ti coordination is very sensitive to chemical or physical parameters and that, at a 
given composition, Ή might behave differendy in a melt compared to a glass. 
The XANES spectrum of a melt of ^S i jT iOi i composition, obtained at 1300 °C 
following heat treatment in the HTC at temperatures up to 1450 °C is compared with the room 
temperature of the glass in Fig. 4. The broad features of the spectra are similar but details 
differ. The relative intensity of the pre-peak remains high in the high-temperature liquids, 
consistent with the coordination number intermediate between 4 and 6 for Ίι 4* in the liquid as 
in the glass. 
These examples testify the broad application field of in-situ high-temperature XAS 
analysis. Expecially regarding the study of melts, of geological as well as technological 
relevance, this device will allow to obtain structural information not suitable to be obtained by 
other methods. 
4955 4978 5002 5026 5050 
Energy (eV) 
Figure 4: XANES spectra of a K2Si4TiOn composition as quenched glass at room 
temperature (top) and as liquid at 1300 °C. (bottom). 
A High-Temperature Device for In Situ Measurement of X-Ray Absorption Spectra 121 
Acknowledgements 
Financial support was given by P.S. CNJfc. "Metodi cristallografici avanzati", by Bayerisches 
Geoinstitut, Deutsche Forschungsgemeinschaft and Fonds der chemischen Industrie. Setup of 
die cell and first experiments were carried out by F.S. while being on sabbatical leave from 
University of Bayreuth to that of Rome. We all thank the staff of PULS, Frascati, for their 
cooperation and S. Priori (Frascati), R. Weigel and G. Herrmansdörfer (Bayreuth) for 
technical support 
References 
[1] F. Röthlisberger, F. Seifert, and M. Czank. Eur. J. Mineral., 2,585-594 (1990). 
[2] C Van Heurck, G. Van Tendeloo, and S. Amelinckx. Phys. Chem. Minerals, 18,441-452 
(1992). 
[3] A. Bianconi. In "EXAFS and Near Edge Structure" (Eds. A. Bianconi, L. Incoccia and S. 
Stipcich). Springer, Berlin, 118-129 (1983). 
[4] S. L. Webb, C R. Ross Π, and J. liebertz. Phys. Chem. Mineral 18,522-525 (1992). 
[5] A. Mottana, E. Paris, G. Delia Ventura, and J.-L. Robert Rend. Uncei Sc. Fis. 9,1, 387-
392(1990). 
[6] T. Dumas, and J. Petiau. / . Non-Cryst. Solids, 81,201-220 (1986). 


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A high-temperature device for in situ measurement of X-ray adsorption spectra

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