The primary elements used for surface mount capacitors are tantalum and niobium. Each has there pros and cons. Though tantalum has the highest capacitance density, it will burn on failure, whereas niobium doesn't. Niobium is also considerably less expensive and more readily available, but can never match the capacitance density offered by tantalum.
Characteristics of surface mounted capacitors:
Made from tantalum or niobium
High price and small size
Wide temperature range and high temperature resistance
Low current and insufficient voltage resistance
Tantalum capacitors will burn out once they fail
Key Material Properties:
Fast cure for high throughput
New materials are developed without halogens
CTE should be between 20-22ppm