Elucidating the structural properties and reversible regional texture effect of GdB6 under high pressure

Highlights: ●GdB₆ is extremely stable under high pressure. ●Contrary to most other materials, the smooth X-ray diffraction rings of GdB₆ become spotty under high pressure. ●High-pressure spotty diffraction rings of GdB₆ are caused by the regional texture effect, which is reversible. ●Grain rotation behavior motivated by stress difference dominates the regional texturing in GdB₆. -- Abstract: As hard and refractory materials with high chemical resistance and mechanical strength, lanthanide hexaborides (LnB₆) have attracted much attention. Among the family of LnB₆, gadolinium hexaboride (GdB₆) occupies a special position due to the half-filled 4f shell of Gd. Here, using in situ synchrotron radiation angle-dispersive X-ray diffraction in a diamond anvil cell at room temperature, the structural stability and compression behavior of GdB₆ are investigated extensively, GdB₆ is observed to be structurally stable up to 73 GPa, and the bulk modulus of 177 GPa is obtained under hydrostatic compression. In this paper, an interesting observation of pressure-induced spotty diffraction rings of GdB₆ is reported, its formation mechanism can be well described by the reversible regional texture effect, which highlights the rearrangement of crystal grains under high pressure. The rearrangement mechanism has been well explained by investigating the pressure dependence of full width at half maximum, macro-differential stress and grain size. Collective grain rotation behavior motivated by stress difference is critical for the rearrangement process, the strong isotropy and strong stability of GdB₆ structure also provide necessary conditions for high-pressure grain rotation behavior. These results will help to promote the understanding of high-pressure structural properties of GdB₆, and provide novel insights on the high-pressure grain behavior in hard materials with strong isotropy and three-dimensional skeleton constituted of strong covalent bonds.