What are the key differences between Tantalum and Tantalum Polymer capacitors?
Conventional MnO2 tantalum capacitors are the ideal choice for applications with requirements for high temperatures (currently up to
175C), high voltage (up to 50V) and established reliability. The
technology offers highest CV in a small package. It’s possible to use
them up to 80% of rated voltage, but in low impedance circuits further
derating needs to be applied - see 7].
Tantalum Polymer Capacitors are
the best choice for consumer applications with low ESR requirements
such as DC/DC converters in notebooks, PDA, telecom and other
applications. The parts can be used up to 80% of rated voltage.
Manufacturer’s specifications of lead-free reflow process capability,
temperature range ratings, leakage current and appropriate
storage/handling in accordance to the MSL level should be verified for
specific application needs.
NbO OxiCapTM Capacitors offer the safest,
available alternative among the various capacitor technologies with
good cost-versus-performance value. The parts can be used up to 80% of
rated voltage and are compatible with lead-free reflow requirements.
The excellent steady state reliability makes these parts a favorite
choice not only for consumer applications but also for high end,
automotive, computer and professional designs. Appropriate temperature
derating needs to be applied for temperatures over 85°C.

http://www.avx.com/docs/techinfo/New_Tantalum_Technologies.pdf