Percolative nature of the transition from 60 K to 90 K phase in YBa2Cu3O6+d

We have measured the heat capacity of YBa2Cu3O6+d for 0.7<d<0.8 between 1.8 and 300K. It was found that doping dependences of specific heat jump and temperature of heat capacity jump contradict to the assumption of spatially homogeneous electronic density. The results suggest that the transition from 60K to 90K phase has a percolative nature and the structure of underdoped 60K phase can be considered as array of superconducting nanoclusters embedded in the insulating matrix.Comment: Submitted to proceedings of M2S-IX 2009, Tokyo (Physica C

Phase transitions and exchange interactions in the SmCr

Spectroscopic investigation and specific heat and magnetic susceptibility measurements of SmCr3(BO3)4 crystals were performed. The spectra of the Sm3+ and Cr3+ ions in samarium chromium borate were calculated and parameters of the exchange interactions between the nearest chromium ions, chromium and samarium ions were determined. Three phase transitions were observed at the temperatures T1 = 7.8 ± 0.5 К, T2 = 6.7 ± 0.5 К, and T3 = 4.3 ± 0.2 К, their nature is discussed. The crystal structures with different space symmetry groups R32 and C2/c were found to coexist in a SmCr3(BO3)4 single crystal