| Germanium dioxide (GeO2) is an important group-IV oxide with multiple crystalline polymorphs. Among them, β-quartz-type GeO2 has attracted considerable attention due to its relatively high dielectric constant, excellent optical transparency, and good thermal stability, making it a promising candidate for applications in optical devices, microelectronic packaging, and high-frequency dielectric materials. However, β-quartz-type GeO2 is generally stable only at relatively high temperatures, and its controllable synthesis and morphology regulation under mild conditions remain challenging. Therefore, understanding the structural transformation mechanism from α-GeO2 to β-GeO2 at relatively low temperatures is of great significance for tailoring the structure and properties of germanium oxide nanomaterials.In this work, commercial α-GeO2 powder was used as the precursor to synthesize GeO2 nanocrystals via a solvothermal method at 180 °C. Polyvinylpyrrolidone (PVP) was introduced as a structure-directing agent to regulate crystal growth behavior through molecular adsorption, enabling the controllable synthesis of β-quartz-type GeO2 nanocrystals. X-ray diffraction (XRD) analysis combined with Rietveld refinement indicates that the initial α-GeO2 gradually undergoes a displacive phase transformation during the solvothermal process, leading to the formation of β-quartz-type GeO2 nanocrystals with a hexagonal crystal system and a space group of P3221. Raman spectroscopy reveals the emergence and significant enhancement of a characteristic vibrational peak at 486 cm?1, indicating a rearrangement of the connectivity among GeO4 tetrahedral units. The rotation of tetrahedra and adjustment of bridging angles promote the formation of a more ordered quartz-like framework.Scanning electron microscopy (SEM) observations further demonstrate a pronounced morphological evolution during the reaction process. At the initial stage, the products mainly consist of irregularly aggregated nanoparticles. As the reaction proceeds, a dissolution–recrystallization process occurs, and under the regulating effect of PVP molecules, the crystals preferentially grow along specific crystallographic orientations. As a result, spindle-like or polyhedral nanocrystals with relatively uniform size distribution are gradually formed.The results indicate that the synergistic effect of solvothermal conditions and surface-active molecules enables the controllable preparation of β-quartz-type GeO2 nanocrystals at relatively moderate temperatures, yielding nanostructures with uniform morphology. This work not only provides a feasible strategy for the low-temperature structural regulation of quartz-type oxide nanocrystals but also offers important insights into the intrinsic mechanism by which molecular adsorption governs phase transformation and morphological evolution in oxide nanocrystals. These findings may further contribute to the controlled synthesis of functional oxide nanomaterials with tailored structures and properties. |
