I assume you are looking for piano quartets for the standard piano and string trio arrangement. Some of my favorites are the Brahms piano quartets. I can't think of any Russian ones right now, unfortunately, but I'll keep thinking. As far as a piano quartet written after 1950, it becomes increasingly harder to find a piano quartet written for the standard piano and string trio arrangement. However, there is a really nice piano quartet written by Latvian composer Pēteris Vasks. It's a six movement piece with some length to it, but you can pick one of them. I'll see if I can think of any more recent ones.