A heat-insulating layer has a melting point above 2500° C., a thermal expansion coefficient in excess of 8×10−6 K−1, and a sintering temperature greater than 1400° C. This material has a perovskite structure of the general formula A1+r(B′1/2+xB″1/2+y)O3+z in which: A=at least one element of the group (Ba, Sr, Ca, Be), B′=at least one element of the group (Al, La, Nd, Gd, Er, Lu, Dy, Tb), B″=at least one element of the group (Ta, Nb), and 0.1