STUDY ON THE THERMAL-BEHAVIOR AND SPECIFI C-HEAT OF DILITHIUM TETRAHYDROBERYLLATE, LI2BEH4

The thermal behavior of dilithium-tetrahydridoberyllate Li2BeH4 has be en studied up to 825 K by simultaneous DSC-TGA measurements. A solid-s olid transition between the hexagonal phenakite form (Be2SiO4) previou sly described and a possible high-temperature cubic form (Li2SO4-HT) o ccurs at 536+/-2 K, In addition the thermal decomposition has been cha racterized by measuring the mass of gas released during heating up to 1075 K. Two distinct steps in the temperature ranges 545-575 K and 905 -935 K indicate a total loss of two moles of hydrogen per mole of hydr ide. The variation of specific heat against temperature has been measu red in the 180-420 K range by differential microcalorimetry. A weak bu t reproducible and reversible anomaly can be detected in the 320-350 K range. This anomaly is marked by a change in the slope of the C-p, vs . T curve. The change in the slope clearly corresponds to a maximum in the vicinity of 340 K on the C-p/T vs T representation, This thermody namic behavior could be interpreted as a superconductivity criterion w hen correlated with magnetic irreversibilities previously observed for the same compound, Thus, LiBe2H4 could appear like a type-II supercon ductor with a critical temperature T-c=(340+/-10) K, However this rema rkable potential property requires resistivity measurements to be defi nitely established, (C) 1998 Elsevier Science B.V.