Physicochemical investigation of shrimp fossils from the Romualdo and Ipubi formations (Araripe Basin).

The Ipubi and Romualdo Formations are Cretaceous units of the Araripe Basin (Santana Group). The first and most ancient was deposited in a lake environment, and some fossils were preserved in shales deposited under blackish conditions. The second was deposited in a marine environment, preserving a rich paleontological content in calcareous concretions.

Temperature- and pressure-induced phase transitions in the metal formate framework of [ND₄][Zn(DCOO)₃] and [NH₄][Zn(HCOO)₃].

Vibrational properties and the temperature-induced phase transition mechanism have been studied in [NH4][Zn(HCOO)3] and [ND4][Zn(DCOO)3] metal organic frameworks by variable-temperature dielectric, IR, and Raman measurements. DFT calculations allowed proposing the detailed assignment of vibrational modes to respective motions of atoms in the unit cell. Temperature-dependent studies reveal a very weak isotopic effect on the phase transition temperature and confirm that ordering of ammonium cations plays a major role in the mechanism of the phase transition.