How can i show author avatar at Post (single) page ?

I tried to get avatar at single (post) page by these codes

<?php
   echo get_avatar( $id_or_email, $size = '96' );
   ?>

<?php echo get_avatar( $comment, 32 ); ?>

<?php echo get_avatar( $id_or_email, $size, $default, $alt ); ?>

<?php echo get_avatar( get_the_author_email(), '60' ); ?>

But no success, nothing get working. It always show default gravatar. Actually author have avatar at gravatar. But not show.

Can anyone please tell me correct ways to display avatar at single post page ?