Yes there are.
Aluminium Oxide is one of the main ceramic bases used by power module manufacturers (along with AlSiC, AlN). It is always recommended to include a Thermal Interface Material (TIM) to manage the "roughness" of the modules base and the heatsink.
The article from Semikron, a module manufacturer who uses Alumina, talks about the need for TIM.
https://www.semikron.com/about-semikron/news-press/detail/miniskiip-anticipating-the-future-for-20-years.html
The benefits these components boast in terms of Rth(j-s) and output
current capability are tremendous. Based on MiniSKiiP housing size 3
with six-pack topology, a typical motor drive application has been
simulated. The replacement of the standard TIM with HPTP (High Performance Thermal Paste) on the
existing module on an Al2O3 substrate brings about a 34%reduction in
the Rth(j-s)by. In a standard motor drive application operating 4kHz
with an overload of 200% for 10s, the result is a remarkable 20%
higher output current at the same junction operation temperatures
There will be equivalent articles from Cree, Infineon, OnSemi ...
If you can, use a graphite sheet. This is an extremely good TIM spreading the losses in the x-y plane to maximise the heatsink utilisation