Thermally stable polycrystalline diamond and methods of making the same

A method of making a cutting element, comprising:

• subjecting at least one layer comprising a premixture of diamond particles and a carbonate material throughout the at least one layer to high-pressure high-temperature sintering conditions, the at least one layer having a non-uniform distribution of diamond particles and carbonate material in the premixture through a thickness of the at least one layer, to form a sintered carbonate-polycrystalline diamond body having a diamond matrix of diamond grains bonded together and carbonates residing in the interstitial regions between the diamond grains, the carbonates having a non-uniform distribution throughout the diamond matrix such that a first region and a second region are formed;
• and
• subjecting the carbonate-polycrystalline diamond body further to a controlled temperature, a controlled pressure, or a combination thereof, to effect an at least partial decomposition of the carbonate material.