The existence of thermal transformations in silver and thallium chromate has been confirmed by differential thermal analysis, temperature-variable X-ray diffraction, and electrical conductivity measurements. The disputed transition ∼330 °C in Tl2CrO4has been shown to be due to lattice distortion. The subtle difference in behavior of the pre-annealed and un-sintered samples is brought out by a variety of experimental measurements. The high temperature structure of these chromates is hexagonal. The presence of small amounts of Tl in Ag2CrO4affects the transition temperature, enthalpy, and the order of the transformation.