Uniaxial vs triaxial compression/decompression and sample environment. Fig. shows the powder X-ray diffraction patterns of recovered samples # 1-6. Only in the case of pyrolytic hBN capsule and triaxial compression was it possible to recover pure rs-ZnO phase (# 1). Either uniaxial compression with the same capsule (# 4) or different sample environments with triaxial compression (# 2-3) do not show such an effect. It is also interesting to note that MgO (capsule of experiment # 3) does not affect the recovery even though it is isostructural to rs-ZnO and is known to stabilize rs-ZnO nanoparticles in the form of nanocomposite. At this point it should be mentioned that neither cBN nor hBN are isostructural to rs-ZnO.