Polymeric nitrogen is an ideal high energy density material.In this work,molecular nitrogen was compressed to 136 GPa at room temperature,and a three-dimensional network of cubic polymeric nitrogen cg-N bonded by a covalent N-N single bond was successfully synthesized by laser heating to 2000 K.The vibrational properties of cg-N lattices were studied by the temperature-dependence on Raman spectra between 173 K to 300 K using a self-designed high-pressure cryogenic device.It was observed that the A-mode phonons of cg-N had different responses to temperature at different pressures.With the temperature decreasing,the blue-shift and temperature-dependence Raman spectra of the A-mode frequency could be well fitted using a model involing multi-phonon decay processes.Our fitting indicated that the three-phonon decay processes were dominated over the four-phonon ones at low temperatures.The three-phonon decay processes at 133 GPa dominated less than it at 140 GPa,while the four-phonon decay processes at 133 GPa dominated more than it at 140 GPa.