Preparation, uniaxial negative thermal expansion and Raman study in semiconductor oxide Nb2WO8 ceramic

Negative thermal expansion materials exhibit important promising to tailor thermal expansion due to their abnormal thermal shrinkage characteristics. Here, the Nb2WO8 ceramic has been synthesized, which exhibits axial negative thermal expansion (αa = −2.05 × 10−6 K−1) from 300 to 1000 K without water absorption or phase transformation. Along a axis, the one O atom is located between two identical Nb atoms and the Nb–O–Nb atomic linkages are formed, in which the Nb2–O2–Nb2 bond angle decreases upon heating, resulting in the negative thermal expansion of a axis. Although the b axis and c axis show positive thermal expansion, the low thermal expansion (αl = 2.30 × 10−6 K−1, 173–1073 K) occurs in unit cell volume due to the negative thermal expansion of a axis. The variable pressure Raman shows that the translational and rotational modes of the polyhedron play a key role in axial negative thermal expansion. This work shows potential application prospects of Nb2WO8 as a low thermal expansion semiconductor ceramic.