Rare earth elements (REEs)
06.01.2026Rare earth elements (REEs) are essential not only for high‑performance permanent magnets, but also for another important, though far less recognized, application: their use as dopants in multilayer ceramic capacitors (MLCCs).
MLCCs are compact, high‑reliability capacitors made by stacking alternating layers of ceramic materials (such as barium titanate, BaTiO3) and metal electrodes, then sintering them into a monolithic block. They are the most widely used capacitor type in modern electronics because they offer high capacitance‑per‑volume, excellent frequency characteristics, and long-term stability. MLCCs appear in virtually all electronic systems, including smartphones, computers, automotive control units, and industrial equipment. They are essential in military and defense electronics such as radar, communications, guidance, and electronic warfare platforms.
REEs are used as dopants in MLCCs to precisely tailor the properties of barium‑titanate‑based dielectrics. Often used REEs for this application are neodymium (Nd), holmium (Ho) and yttrium (Y). Especially neodymium is the REE of choice in MLLCs. The ionic radius of Nd3+, almost exactly at midway between those of Ti4+ and Ba2+. Nd appears to substitute equally at both Ba and Ti sites in BaTiO3. The REE ions control grain growth during sintering, reduce oxygen‑vacancy defects, improve the lifetime under electric stress and tune the Curie temperature of the ferroelectric material. These effects that are essential for achieving the desired capacitance, temperature behavior, and long‑term durability of MLCCs.
Permanent magnets use REEs in large, bulk quantities, typically 25–35 wt% in Nd‑Fe‑B, so each kilogram of magnet contains hundreds of grams of REEs. In MLCCs, by contrast, REEs are added only as trace dopants, usually around 0.1–2 mol% of the BaTiO3 dielectric, resulting in microgram‑level REE content per capacitor. Even though MLCCs are produced in enormous volumes, their total REE consumption is tiny compared with the large amounts required for permanent magnets. Nevertheless, the application of REEs in MLCCs for civil and military applications is strategically very important.
SOLVOMET R&I CentreSIM2 KU Leuven