If someone recites an Aayah (Verse) of Sajdah from Qur'an during prayer then it becomes obligatory to perform the Sajdah-e Tilawah immediately.
If someone recites an Aayah (Verse) of Sajdah outside of prayer then Sajdah-e Tilawah is not required immediately. Rather one may perform the Sajdah for Tilawah later as well.
When there is a large congregation of people such as during the time of Friday prayer or Eid prayer, scholar advise that the Imam should avoid reciting the Aayah of Sajdah as many people may get confused and either miss it entirely or lose the concentration in prayer due to such confusion.
Therefore, it is advisable for an Imam that he should not recite an Aayah of Sajdah during Fridah prayer. However, if an Imam did recite an Aayah of Sajdah then the Sajdah-e Tilawah would become necessary and must be performed immediately.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America