By examining the nucleation and growth phenomena for Hgl(2) crystals in physical vapor transport ampoules with a variation of temperatures of the source powder side T-sou and of the crystal growth side Tory. both are near its solid-solid phase transition temperature T-c = 127 degrees C, our experimental results reveal that under T-cry < T-c: (1) the solid (alpha or beta) phase structure of the as-grown Hgl(2) crystal is surprisingly governed by T-sou; (2) the temperature range of existence for the metastable beta-Hgl(2) phase in crystal growth side is about 17 degrees C below T-c; and (3) by turning a rotating motor to act as mechanical perturbations, this temperature range of existence for p-phase now reduces to about 11 degrees C below T-c. To explain these phenomena, especially for the metastable beta-phase formed at T-cry < T-c, a model based on an existence of the vaporized Hgl(2) clusters in vapor transport region with specific nanostructure dominated by T-sou is proposed. (c) 2006 Elsevier B.V. All rights reserved.