This paper reports on the behavior of single crystal Tb₅Si_2.2Ge_1.8 in the vicinity of its order-disorder and order-order phase transition from a higher temperature paramagnetic∕monoclinic state to a lower temperature ferromagnetic∕orthorhombic state. Measurements have been made of thermal and field induced changes in strain along the crystallographic a axis. The material exhibits large strains of up to 1500 ppm when a magnetic field is applied to it in its paramagnetic state but much smaller strains when a field is applied to it in its ferromagnetic state. These field induced strains are different from conventional magnetostriction because they result mostly from the change in crystal structure. As a result of this the field induced strain changes that accompany the phase transitions of this material are not fully reversible. The shape and slope of the strain versus magnetic field curves were distinctly different depending on whether the material started from above the Curie temperature (where the application of a magnetic field of sufficient strength induced a structural phase transformation) or started from below the Curie temperature (where the application of a field merely stabilized the existing magnetic order).