One of the domes of the ‘Orta Sofa’ (Middle hall). To make the connection between the dome and the walls ‘Turkish triangles’ were used instead of the usual ‘pendentives’.

A ‘pendentive’ is a constructive device permitting the placing of a circular dome over a square room (or an elliptical dome over a rectangular room). The pendentives, which are triangular segments of a sphere, taper to points at the bottom and spread at the top to establish the continuous circular or elliptical base needed for the dome. In masonry the pendentives thus receive the weight of the dome, concentrating it at the four corners where it can be received by the piers beneath. The pendentive was introduced by the Romans (around 200 AD) and fully used by the Byzantines.

The ‘Turkish triangle’ was a new pendentive: a transformation of the curved space of the traditional pendentive into a fanlike set of long and narrow triangles built at an angle from each other. It was introduced in Anatolia by the Seljuk.

Correspondent: J.M.Criel, Antwerpen.
Source: ‘Islamic Architecture: Ottoman Turkey’ (Godfrey Goodwin) – London 1977 - Wikipedia
& Encyclopaedia Brittanica .