International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 2.6, pp. 151-153

Section 2.6.6. High-temperature sample stages

C. A. Reissa*

aNoordikslaan 51, 7602 CC Almelo, The Netherlands
Correspondence e-mail: Celeste.Reiss@PANalytical.com

2.6.6. High-temperature sample stages

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A typical laboratory non-ambient setup consists of a non-ambient sample stage, often called a temperature chamber. The sample stage is mounted on a goniometer, preferably in a θ–θ configuration (Fig. 2.6.2[link]). In this case the sample stays horizontal and there is no need to fear melting of the sample with the possibility of it dripping off/out of the sample holder.

[Figure 2.6.2]

Figure 2.6.2 | top | pdf |

An Anton Paar HTK 1200N high-temperature oven chamber on a PANalytical Empyrean system equipped with a PIXcel3D detector.

A temperature-control unit, vacuum equipment, gas supply and water cooling have to be added to the system before it can be operational.

2.6.6.1. Direct heating: strip heaters

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The highest temperatures can be reached with so-called strip heaters (Fig. 2.6.3[link]). Commercial stages that can heat to up to 2573 K are available. Sample heating is performed with a high-current resistance heater. The specimen is placed directly on the strip or in a crucible on the strip. Typical strip materials are platinum (which can be heated in air to up to 1873 K) and tungsten (maximum temperature 2673 K), which requires a vacuum or an inert-gas atmosphere. Less common strip materials which have to be operated in vacuum or in an inert-gas atmosphere are graphite (maximum 1773 K), molybdenum (maximum 2173 K) and tantalum (maximum 2873 K). In addition to very high temperatures, these heaters offer very fast heating and cooling. The HTK 2000N from Anton Paar, for example, can reach up to 2573 K in 3 min. The temperature is measured with a thermocouple, which is usually welded to the heating strip. The main disadvantages of strip heaters are possible chemical reactions between the heating strip and sample, difficulties in measuring the sample temperature accurately and difficult sample preparation. Often, it is not the starting material that reacts but the products that form during heating. Another strip material can be chosen if reactions are known to occur. Inaccurate temperature measurements can be minimized by placing a second temperature sensor on top of the sample.

[Figure 2.6.3]

Figure 2.6.3 | top | pdf |

The interior of a typical strip-heater sample stage (Anton Paar HTK 2000N) with heating strip (A), mechanics to compensate strip expansion (B), thermocouple wires (C), heat shield (D) and water-cooled base plate (E).

2.6.6.2. Environmental heating: the oven

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The second common type of sample stage for high temperatures are oven heaters, also called environmental heaters (Fig. 2.6.4[link]). An electrically heated wire is formed into a cage, which is surrounded with thermal insulation. The heater and insulation form a furnace which almost completely surrounds the sample, creating a very uniform temperature distribution on the inside and minimizing the heat transfer to the housing of the sample stage. Heat is transferred via radiation and convection to the sample. The sample is placed on a sample holder in the centre of the furnace, without direct contact with the heater. The sample temperature is measured with a thermocouple located close to the sample, providing accurate measurement of the sample temperature. In addition, it is possible to oscillate the sample to improve the data quality (by reducing granularity), and the user can measure (polycrystalline) solid samples as well as powder samples. In most cases, a long sample holder must be used to place the sample in the centre of the furnace. The thermal expansion of the sample holder while heating must be compensated for by z adjustment to avoid sample displacement (see Section 2.6.4.5[link]). Windows for letting the X-rays enter and leave the chamber should preferably have no influence on the diffraction process. Different materials are available depending on the requirements of the non-ambient measurements. Kapton is the most commonly used window material, followed by graphite, aluminum and beryllium. Environmental heating is also one of two methods used to heat capillaries for X-ray diffraction with transmission geometry. The other option is heating the capillary with a gas flow.

[Figure 2.6.4]

Figure 2.6.4 | top | pdf |

A typical furnace heater (Anton Paar HTK 1200N) consisting of sample holder (A), heater (B), thermal insulation (C), water-cooled housing (D), thermocouple (E) and X-ray window (F).

Example: Cement. Cement consists of different calcium silicates (see Chapter 7.12[link] ). The exact phases that are present and their abundances determine important physical properties of a cement such as its strength. One of the phases in cement, belite (Ca2SiO4), exhibits rapid phase transitions. Fast transitions require good time resolution to detect short-lived intermediate phases and to follow the kinetics of fast phase transformations. An Anton Paar HTK 1200N oven was used for this experiment together with a PIXcel3D detector in static mode using a radius-reduction interface to allow snapshots to be taken over a 2θ range of 6° within a time frame of less than 1 min. Bragg–Brentano geometry was used to achieve a good resolution in 2θ and, to compensate for thermal expansion of the sample holder, an automatic height compensation was applied. On heating CaCO3 with amorphous SiO2 at 10 K min−1, a solid-state reaction was seen at 853 K; α′L-Ca2SiO4 is formed together with CO2 (Fig. 2.6.5[link]a). Dicalcium silicate exists in five polymorphic forms (Odler, 2000[link]). During cooling, one of the other polymorphs of dicalcium silicate, β-Ca2SiO4, is formed, which has a different crystal structure and optical properties (Fig. 2.6.5[link]b).

[Figure 2.6.5]

Figure 2.6.5 | top | pdf |

(a) Upon heating, CaCO3 (the peak at about 29.3° in 2θ) reacts with SiO2 (amorphous); at 853 K the new phase α′L-Ca2SiO4 is formed (the peak between 33 and 32° in 2θ). (b) During cooling α′L-Ca2SiO4 (the two peaks between 33 and 32° in 2θ), a different dicalcium silicate polymorph is formed at  773 K; this is β-Ca2SiO4.

2.6.6.3. Environmental heating: lamp furnace

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Another approach to designing an environmental chamber is the quadrupole lamp furnace developed by W. M. Kriven (Sarin et al., 2006[link]). Such a furnace can heat a specimen to >2000 K in air. A recent application of this furnace is the characterization of high-temperature phase transitions in Zr2P2O9 (Angelkort et al., 2013[link]).

2.6.6.4. Domed hot stage

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Sample stages with an X-ray transparent dome, such as the DHS 1100 domed hot stage manufactured by Anton Paar (Fig. 2.6.6[link]), give another dimension to polycrystalline diffraction. The dome is made of highly transparent graphite. The transmission of the primary and diffracted beams depends on the wavelength used, and for Cu Kα radiation 65% is transmitted. The dome can be used on most of the commercially available modern multipurpose X-ray diffractometers with linear or two-dimensional detectors. Mounted on an XYZ table or a cradle, these sample stages can be used to study texture, stress/strain and other phase-induced changes in (for example) thin-film layers under non-ambient conditions.

[Figure 2.6.6]

Figure 2.6.6 | top | pdf |

Sample-heating stage (Anton Paar DHS 1100) with lightweight, air-cooled housing (A), dome-shaped X-ray window (B) and heating plate with sample fixation (C).

Example: thin films. A great deal of research has been devoted to the development of gallium nitride (GaN)-based high-electron-mobility transistor (HEMT) structures (Kelekci et al., 2012[link]; Butté et al., 2007[link]). The structural quality of the layers and their interfaces is critical for the performance of the device (Teke et al., 2009[link]). Detailed knowledge of the effects of further process steps, such as thermal annealing, on these parameters is crucial. X-ray reflectivity can be used for monitoring, among other things, the layer thickness and (interface) roughness (Daillant & Gibaud, 2009[link]). To monitor the annealing process, a wurtzite-type AlInN/AlN/GaN/ heterostructure was mounted on a DHS 1100 domed hot stage; 26 scans were made, each of which lasted 1 h and 59 min at a temperature of 823 K (Fig. 2.6.7[link]). From these reflectivity measurements the activation energy could be calculated and compared with the results from X-ray diffraction data from a nominally identical structure (Grieger et al., 2013[link]). The same value was found for both experiments within 5%, giving valuable information about heterostructure layer and interface stability.

[Figure 2.6.7]

Figure 2.6.7 | top | pdf |

Monitoring of layer thickness and roughness by X-ray reflectivity measurements during annealing at 823 K.

References

Angelkort, J., Apostolov, Z. D., Jones, Z. A., Letourneau, S. & Kriven, W. M. (2013). Thermal properties and phase transition of 2ZrO2·P2O5 studied by in situ synchrotron X-ray diffraction. J. Am. Ceram. Soc. 96, 1292–1299.Google Scholar
Butté, R., et al. (2007). Current status of AlInN layers lattice-matched to GaN for photonics and electronics. J. Phys. D Appl. Phys. 40, 6328–6344.Google Scholar
Daillant, J. & Gibaud, A. (2009). Editors. X-ray and Neutron Reflectivity: Principles and Applications. Berlin, Heidelberg: Springer.Google Scholar
Grieger, L., Kharchenko, L., Heuken, M. & Woitok, J. F. (2013). 15th European Workshop on Metalorganic Vapour Phase Epitaxy (EWMOVPE XV), Extended abstracts, pp. 51–54. Jülich: Forschungszentrum Jülich. Google Scholar
Kelekci, O., Tasli, P., Cetin, S. S., Kasap, M., Ozcelik, S. & Ozbay, E. (2012). Investigation of AlInN HEMT structures with different AlGaN buffer layers grown on sapphire substrates by MOCVD. Curr. Appl. Phys. 12, 1600–1605.Google Scholar
Odler, I. (2000). Special Inorganic Cements. London: CRC Press.Google Scholar
Sarin, P., Yoon, W., Jurkschat, K., Zschack, P. & Kriven, W. M. (2006). Quadrupole lamp furnace for high temperature (up to 2050 K) synchrotron powder X-ray diffraction studies in air in reflection geometry. Rev. Sci. Instrum. 77, 092906.Google Scholar
Teke, A., Gökden, S., Tülek, R., Leach, J. H., Fan, Q., Xie, J., Özgür, Ü., Morkoç, H., Lisesivdin, S. B. & Özbay, E. (2009). The effect of AlN interlayer thicknesses on scattering processes in lattice-matched AlInN/GaN two-dimensional electron gas heterostructures. New J. Phys. 11, 063031.Google Scholar








































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