Plastic deformation tests have been performed at low temperature (T[MATH]450°C) under a confining pressure in order to promote dislocation motion at temperature where samples are usually brittle . A mechanism for plastic deformation by partial dislocations has been evidenced as well as the influence of dopants on the macroscopic plastic deformation. Discrepancies between low temperature plastic deformation under confining pressure and conventional compressive tests conducted in the range of medium temperatures (400°C[MATH]T[MATH]650°C) are discussed