Mono-phase YBa2Cu3O7-x high critical temperature (Tc) superconductor samples were obtained by sintering at 999 °C and 960 °C, respectively, followed by special cooling programs, in oxygen atmosphere. In the framework of XRD diffractometry, we determined the crystallite dimensions and the unit cell parameters for the orthorhombic crystalline system of our samples: a=0.38128 nm; b=0.38814 nm; c=1.16753 nm. A preferential orientation of the crystallites on the sample surface, with c axis along the pressure axis is observed. The fitting equation from ref. [3], giving the oxygen content, (7-x), over the c-axes values of YBCO-123 structures (belonging only to Pmmm spatial group), delivered by ICSD Data Base, allowed us to estimate a value, (7-x), of 6.88 for our YBa2Cu3O7-x samples. On cooling to nitrogen liquid temperature, both resistive and diamagnetic measurements indicate some differences between the superconductor parameters (critical temperature, residual resistivity, crossover temperature from 3D-2D dimensionality and coherence length) [1,2], depending on the sample preparation program. Results of the thermogravimetry (TG) on heating, in air atmosphere (an increasing rate of 10 K min-1), from room temperature (RT) to 1004.99 °C, show the following behavior: a very small mass increase (of 0.101%) from RT to 450 °C probably due to O2 chemical adsorption, than a mass decrease of 1.208 % in the temperature range from 450 °C to 1004.99 °C when a part of oxygen content is lost, until (7-x)=6.80 at 934 °C. We interposed three isotherms in the cooling process (of 10 K min-1 rate): at 950 °C for 1h, at 750 °C for ½ h, and at 450 °C for 5 h. A strong oxygen accumulation occurred during the last two isotherms (at 750 °C and at 450 °C), the final oxygen content (7-x) acquired at 463.15 °C being of = 6.95, improving also Tc. In argon atmosphere, during a complete thermal cycle (heating and cooling), a different behavior is encountered. It begins with a mass increase of 0.707 %, on heating from RT to 429.3 °C, due to Ar adsorption; then the mass decreased with 1.116 % in the heating range from 429.3 °C to 730.7 °C; it follows another mass increase of 0.533 % from 730.7 to 931.1 °C. From 931.1 °C to 998.9 °C, the mass decreases with 1.092 %, accompanied by an endothermic process in two steps, evidenced on DSC, and DTA curves, due to a solid-solid transition from orthorhombic to tetragonal YBCO crystalline systems, followed by sample melting and Ar desorption.