Is it from the Sunnah to raise one's voice with the takbir when rising from prostration in the last rak'ah to inform the congregants of it?

There is no basis in the Sunnah for some imams to lengthen the takbir when sitting for the tashahhud in order to alert the congregants, nor has any scholar ever stated that the tashahhud sitting should be specifically marked by a lengthened takbir for this reason. What some scholars have said is that it is desirable to lengthen all takbirat al-intiqal (transitionary takbirs), but this opinion has no evidence to support it. Sheikh Ibn 'Uthaymeen mentioned that what imams do, which is not differentiating between the takbirs, is the apparent Sunnah, and they should not be criticized for it. He also stated that the confusion of the congregants is usually due to their heedlessness.