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@INPROCEEDINGS{Sohn:850086,
      author       = {Sohn, Yoo Jung and Mauer, Georg and Roth, Georg and
                      Guillon, Olivier and Vassen, Robert},
      title        = {{B}-site ordered double perovskite,
                      {L}a2({A}l0.5{M}g{T}a0.5){O}6 for thermal barrier
                      applications and its high-temperature phase transition},
      reportid     = {FZJ-2018-04167},
      year         = {2018},
      abstract     = {An improvement of gas turbine engines can be obtained by
                      increase of the inlet temperatures. The standard thermal
                      barrier coating (TBC) material yttria partially stabilized
                      zirconia (YSZ) decomposes at elevated temperatures into
                      high-yttria and low-yttria phases. The latter transforms
                      upon cooling into the monoclinic phase with an associated
                      large volume increase, which may result in failure of the
                      TBC [1]. Thus, new TBC materials are widely searched to
                      further improve the gas turbine engine efficiency at
                      long-term operation temperatures above 1200 °C. Over the
                      last decades a large amount of candidates have been
                      investigated to identify alternative TBC materials. Among
                      them, the complex rare-earth perovskites gained interest due
                      to their high melting point and possible tailoring
                      properties with B-site cation ordering effect [2,3].
                      Recently, plasma sprayed La2(Al0.5MgTa0.5)O6 (LAMT) coatings
                      showed significantly improved thermal cycling lifetime
                      results, and were suggested to be a promising candidate
                      [4,5]. Up to now, synthesized LAMT-powder was identified to
                      be an orthorhombic phase with the space group symmetry,
                      Pnma, which is isostructural to orthorhombic LaFeO3. The
                      Pawley refinement on the measured powder X-ray diffraction
                      (XRD) data revealed no oddity. However, a strong mismatch of
                      the peak intensities was detected during the Rietveld
                      analysis. A possible texture effect was excluded because of
                      the powder morphology, as well as, by trying out the
                      different sample preparation methods. To clarify the correct
                      crystal structure of LAMT and to check the phase stability,
                      in-situ high-temperature XRD was carried out in the
                      temperature range of 25-1200 °C. Unlike reported earlier
                      [4], a structural phase transition was observed at ~ 855 °C
                      upon heating, and this phase transition was completely
                      reversible. The crystal structure of LAMT was then refined
                      by Rietveld analysis in the monoclinic space group symmetry,
                      P21/n [6] at room temperature, with β = ~ 90°. In the
                      monoclinic crystal structure, the B-site cations are
                      ordering in a rock-salt type arrangement. The Mg2+-ions take
                      the fully occupied 2c-Wyckoff position whereas the Al3+- and
                      Ta5+-ions occupy each half of the 2d-Wyckoff position. The
                      crystal structure of LAMT becomes rhombohedral with the
                      space group, R-3 above ~ 855°C. The unit cell volume
                      changes gradually as a function of temperature without any
                      abrupt jump. [1] Vaßen R., Jarligo M.O., Steinke T., Mack
                      D.E. and Stöver D. Surf. Coat. Technol., 2010, 205, 938.
                      [2] Guo R., Bhalla A.S. and Cross L.E. J. Appl. Phys., 1994,
                      75, 4704. [3] Tarvin R. and Davies P.K. J. Am. Ceram. Soc.,
                      2004, 87, 859. [4] Jarligo M.O., Mack D.E., Vaßen R. and
                      Stöver D. J. Therm. Spray Technol., 2009, 18, 187.[5]
                      Schlegel N., Sebold D., Sohn Y.J., Mauer G. and Vaßen R. J.
                      Therm. Spray Technol., 2015, 24, 1205.[6] Kim Y.I. and
                      Woodward P.M. Solid State Chem., 2007, 180, 2798.Keywords:
                      thermal barrier coatings, ordered double perovskite, in-situ
                      high-temperature XRD},
      month         = {Jul},
      date          = {2018-07-01},
      organization  = {The 16th European Powder Diffraction
                       Conference, Edinburgh (U.K.), 1 Jul
                       2018 - 4 Jul 2018},
      subtyp        = {Other},
      cin          = {IEK-1 / JARA-ENERGY},
      cid          = {I:(DE-Juel1)IEK-1-20101013 / $I:(DE-82)080011_20140620$},
      pnm          = {113 - Methods and Concepts for Material Development
                      (POF3-113)},
      pid          = {G:(DE-HGF)POF3-113},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/850086},
}