The simultaneous decomposition of strontium carbonate that occurs during the solid-to-solid phase transition is a detriment to the use of this material as a high temperature standard for DTA. An atmosphere of carbon dioxide is shown to deter the reversible decomposition to much higher temperatures where it is no longer a problem. The phase transition temperature was observed to shift during the initial heating through the transition in carbon dioxide but remain constant thereafter. Changes were also observed in the X-ray diffraction pattern during the initial heating. It is proposed that the use of this material as a DTA standard be restricted to an atmosphere of carbon dioxide using a sample that has undergone at least one temperature cycle in that atmosphere.