Anisotropic heat conduction in the metal organic framework perovskites [C(NH2)3]X(HCOO)3 (X = Cu, Zn)

We report thermal conductivity (κ) measurements on single crystals of the metal-organic framework perovskite compounds [C(NH2)3]X(HCOO)3 (X = Cu, Zn) in the temperature range 5 K ≤ T ≤ 300 K. The directionality of N-H⋅ ⋅ ⋅O bonds and their stretching due to the Jahn-Teller distortion in the Cu compound are identified as mechanisms underlying differences in the κ(T) behavior for the two compounds and their anisotropy. For heat flow along a direction preferentially transverse to the N-H⋅⋅⋅O bonds, κ ∼ 0.6 W/mK near 300 K, approaching the theoretical minimum value. A possible magnetic contribution to the heat flow in the Cu compound is also discussed.