  Wireless surface acoustic wave (SAW) sensors constitute a promising solution
to some unsolved industrial sensing issues taking place at high temperatures.
Currently, this technology enables wireless measurements up to 600-700$^\circ$C
at best. However, the applicability of such sensors remains incomplete since
they do not allow identification above 400$^\circ$C. The latter would require
the use of a piezoelectric substrate providing a large electromechanical
coupling coefficient K 2 , while being stable at high temperature. In this
letter, we investigate the potentiality of stoichiometric lithium niobate (sLN)
crystals for such purpose. Raman spectroscopy and X-ray diffraction attest that
sLN crystals withstand high temperatures up to 800$^\circ$C, at least for
several days. In situ measurements of sLN-based SAW resonators conducted up to
600$^\circ$C show that the K 2 of these crystals remains high and stable
throughout the whole experiment, which is very promising for the future
achievement of identifiable wireless high-temperature SAW sensors.
