Adding to Lexible's very concise in-universe answer, there are clear themes that Tolkien depicted evil as technology throughout his works. So let's have a look at a few factors that would sit inline with this theory.
Aulë was the Vala whose themes in the music of the Ainur created the physical formation of Arda. Apart from Eru, he is thought to be the father of creation (and certainly by the Dwarves who worship him as a god, since they are his children). Aulë mastered the arts of craft, forging and building, hence why the Dwarves are so attuned to mining and collecting/forging great treasures. Sauron (Mairon) was considered one of his greatest apprentices, and learnt everything from his master before his fall. He was obsessed with order and coordination and disliked waste and confusion, and it was the admiration of Melkor's strength and will that attracted him to become his follower.
It's clear to see that Tolkien was depicting Sauron's character as a metaphor for military regime. After his experiences in the war, and his apparent PTSD, you could understand why he would depict this as evil after the atrocities he witnessed. There's also a clear theme that Sauron's aspirations were initially with good intentions, but because of his blind following of Melkor (the regime), his actions eventually set out to cause disharmony and destruction. Much like a war, where the foot soldiers could be fighting for anything without knowledge. It's not until after the fall of Melkor and the feeling of shame he felt once realising what he had done, that eventually this bred evil thought and darkness.
Tolkien disliked admitting allegory, because in my opinion, he was hiding his thoughts on the real world inside his works, and didn't want people to keep bothering him about it. The clear connections between Saruman/Sauron and forging, building, removing forests and life from areas and generally causing pollution, distress and terrorism in the world is paralleled in our own, the path set out where Sauron had the skills to create terrible war weapons and fortresses shows that technological advancement in Middle-earth is thought of as evil. Where on the other hand, the natural habitats of Lothlórien, Rivendell, and The Shire are depicted as peaceful, good places to live. However, it's also clear that Gondor/Rohan is not included in this, since Tolkien depicted Men to be capable of terrible things if they are corrupted by greed but also capable of good if lead down the right path.
EDIT: So to answer the question directly. Were there any major technological advancements in the Third Age? I'm not sure, but certainly the practical use of these technologies became more apparent. The army of Mordor/Isengard's use of siege weapons is a clear indication of this. Upon the resolution and destruction of Mordor, most of what was "magic" was removed from the earth and the time of men came in the Fourth Age. Since Tolkien believed that he was writing a story within our own timeline and actually Arda is Earth, it would seem reasonable to assume that he was implying we are beyond the Fourth Age now (maybe sixth or seventh actually), and that evil only resides in the free will of men and how they use technology, and no embodiment of evil will exist again until Dagor Dagarath (judgement day).