The Apple A5X is a 32-bit system-on-a-chip (SoC) designed by Apple Inc., introduced at the launch of the third generation iPad on March 7, 2012. It is a high performance variant of the Apple A5; Apple claims it has twice the graphics performance of the A5. It was superseded in the iPhone 5 and 5C by the A6 chip and the fourth generation iPad by the A6X chip.
The A6 chip preceded the A5 chip.
The A5 chip was introduced before the A6 chip, which means the A5 chip preceded the A6, not the other way around.