Abstract <p>The formation conditions and processes of the complex aluminate Dy₂SrAl₂O₇ are studied. It is established that solid-state synthesis of Dy₂SrAl₂O₇ proceeds through the formation of strontium aluminate SrAl₂O₄. At temperatures above 1200°C, active interaction begins between the intermediate compound SrAl₂O₄ and Dy₂O₃, associated with the transition of the two-dimensional nonautonomous phase SrAl₂O₄ into a liquid-like state. The thermal stability of Dy₂SrAl₂O₇ up to the temperature of incongruent melting at 1750°С is characterized for the first time. The coefficient of thermal expansion (CTE) of Dy₂SrAl₂O₇ is experimentally determined to be 8 × 10^–6 K^–1 in the temperature range of 400–1300°С. It is shown that active sintering of Dy₂SrAl₂O₇ begins at 1300°С. A change in the type of melting diagrams is shown in the <i>Ln</i>₂SrAl₂O₇ series, where <i>Ln</i> = La → Gd → Dy, Ho. A decrease in both melting temperatures and CTE values is revealed across the <i>Ln</i>₂SrAl₂O₇ series (<i>Ln</i> = La → Ho).</p>