La-139 NQR and NMR relaxation measurements in the til;le compound have been
used to investigate the dynamical properties of the structural phase trans
itions (SPT): HTT --> LTO and LTO --> LTT of lathanum cuprate. We present t
he data for thermodynamic fluctuations of critical modes in the vicinity of
the SPT's which clearly reveal the character of each SPT and its dependenc
e on doped hole concentration.