thermal conductivity, \(\lambda\)

https://doi.org/10.1351/goldbook.T06299
Tensor quantity relating the heat flux, Jq, to the temperature gradient, Jq = -λ.∇.T.
Source:
Green Book, 2nd ed., p. 37 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)