Grab next post title in archive page

This doesn’t seem terribly efficient but you could just look up the next/prev posts in the loop used to display the post then output the post titles in the nav calls.

// loop
if ( have_posts() ) : while ( have_posts() ) : the_post();

  // ... post display

  // next & prev post data
  $older = get_previous_post();
  $newer = get_next_post();
endwhile; endif;

// pagination
next_posts_link( $older->post_name );
previous_posts_link( $newer->post_name );