Controllable Growth Of PbZr_0.52Ti_0.48O₃ Nanocrystals Prepared By Hydrothermal Method And Their Growth Mechanism

PbZr_0.52Ti_0.48O₃ ferroelectric material is widely applied in the fields of microelectronics and optoelectronics due to its excellent ferroelectric,piezoelectric,and dielectric properties.In order to meet the development requirements of miniaturization and integration of electronic devices,PbZr_0.52Ti_0.48O₃ nanocrystals have attracted much attention.In this dissertation,PbZr_0.52Ti_0.48O₃ nanocrystals were synthesized by the hydrothermal method.The effect of the types of mineralizers,mineralizer concentration,poly(vinyl pyrrolidone)(PVP)content,concentration of precursor solution,reaction temperature and reaction time on growth of PbZr_0.52Ti_0.48O₃nanocrystals were systematically investigated.The main conclusions are listed as follows:Firstly,Pb(CH₃COO)₂,Zr(NO₃)₄ and Ti(OC₄H₉)₄ were used as raw materials with NaOH mineralizer to prepare PbZr_0.52Ti_0.48O₃ nanocrystals by the hydrothermal method.In the 0.05 M precursor solutions,the single-phase PbZr_0.52Ti_0.48O₃ crystals were prepared at 200°C for 20 h with NaOH concentrations of 0.5-2 M.With increasing the NaOH concentration,the grain size of PbZr_0.52Ti_0.48O₃nanocrystals gradually decreased.In the 0.05 M precursor solutions,the PbZr_0.52Ti_0.48O₃ crystals were obtained at reaction temperature of 160-200?for 20 h with NaOH concentration of 1 M.With increasing the reaction temperature,the grain size of PbZr_0.52Ti_0.48O₃ nanocrystals obviously increased.In the 0.05 M precursor solutions,the PbZr_0.52Ti_0.48O₃ crystal were obtained at 200°C for 3-48 h with NaOH concentrations of 1 M.With increasing the reaction time,the grain size of PbZr_0.52Ti_0.48O₃ nanocrystals slightly increased.When the PbZr_0.52Ti_0.48O₃ crystals were prepared with NaOH mineralizer,the atomic ratio of Pb:Zr:Ti was consistent with the stoichiometric ratio of PbZr_0.52Ti_0.48O₃.However,a small amout of Na⁺ions was co-existed with PbZr_0.52Ti_0.48O₃ crystals.Secondly,the effect of PVP on synthesis of PbZr_0.52Ti_0.48O₃ nanocrystals was investigated in the hydrothermal process.Pb(CH₃COO)₂·3H₂O,Zr(NO₃)₄·5H₂O and Ti(OC₄H₉)₄were used as raw materials,KOH was used as mineralize,PVP was used as surfactant,and PbZr_0.52Ti_0.48O₃ nanocrystals were synthesized by the hydrothermal method.In the 0.05 M precursor solution,the uniform PbZr_0.52Ti_0.48O₃ crystals were prepared with PVP concentrations of 6 g/L and KOH concentration of 2 M at 200°C for 20 h.The grain size of PbZr_0.52Ti_0.48O₃ nanocrystals obviously decreased due to the PVP surfactant,which indicated that the PVP surfactant was effective to control the growth of PbZr_0.52Ti_0.48O₃ nanocrystals.In the 0.05 M precursor solution,at the KOH concentration of 2 M and the PVP concentrations of 6 g/L,PbZr_0.52Ti_0.48O₃ crystals were obtained at reaction temperature of 160-200?for 12 h.In the 0.05 M precursor solution,at the KOH concentration of 2 M and the PVP concentrations of 6 g/L,PbZr_0.52Ti_0.48O₃ crystals were obtained at 200?for 4-48 h.In the hydrothermal process,PbZr_0.52Ti_0.48O₃ nanocrystals with several nanometer diameter were co-formed with micrometer-size PbZr_0.52Ti_0.48O₃ crystals.The PbZr_0.52Ti_0.48O₃ nanocrystals were attached on the micrometer-size PbZr_0.52Ti_0.48O₃ crystals based on oriented attachment.The Pb:Zr:Ti ratio of the crystals was consistent with the stoichiometric ratio of PbZr_0.52Ti_0.48O₃.A small amount of K⁺ions was also observed.To solve the contamination of alkali metal ions,the mineralizer of NaOH and KOH was replaced by ammonia.PbTiO₃ nanocrystals were prepared by hydrothermal method,when Pb(CH₃COO)₂ and Ti(OC₄H₉)₄ were used as raw materials with ammonia mineralizer.In the 0.1 M precursor solution,the single-crystal PbTiO₃nanorods were prepared at 200?for 24 h with Pb/Ti ratio of 1.0 and ammonia concentration of 4.4 M.In the 0.1 M precursor solution,at the ammonia concentration of 4.4 M and reaction time of 24 h,the single-phase PbTiO₃ nanocrystals were obtained at reaction temperature of 160–200?.When the reaction temperature was 200°C,the dendritic PbTiO₃ nanorods were formed.In the 0.1 M precursor solution,at the ammonia concentration of 4.4 M,the single-phase PbTiO₃ nanocrystals were prepared at 200?for 12-48 h.With increasing the reaction time,the grain size of PbTiO₃nanorods increased,since the ammonia provided enough OH^-in the precursor solution.The formation of dendritic PbTiO₃ nanorods was based on the oriented attachment mechanism.When two PbTiO₃ nanorods grew in parallel,the(110)plane was preferentially attached.The PbTiO₃ nanorods grew along the[001]c-axis,and the oriented attachment was along the[001]c-axis to form the dendritic PbTiO₃ nanorods.The bottle-neck-like morphology was formed at the junction of PbTiO₃ nanorods.Based on the successful preparation of PbTiO₃ nanocrystals with ammonia mineralizer,PbZr_0.52Ti_0.48O₃ nano cubes were prepared by the two-step hydrothermal method,when Pb(CH₃COO)₂·3H₂O,C₆H₁₈N₂O₈Ti and C₁₂H₂₈O₄Zr were used as raw materials with ammonia mineralizer.In the 0.05 M precursor solution,first-step ammonia concentration of 4.4-6.6 M,at the second-step ammonia concentration of 4.4-6.6 M,the reaction temperature of 200°C and the reaction time of 20 h,the single-crystal PbZr_0.52Ti_0.48O₃ nano cubes were obtained.In the 0.05 M precursor solution,at the first-step ammonia concentration of 4.4 M and the second-step ammonia concentration of 6.6 M,the PbZr_0.52Ti_0.48O₃ nano cubes were prepared at 200°C for 12-24 h.In this paper,we firstly reported the controllable growth of dendritic PbTiO₃nanorods and PbZr_0.52Ti_0.48O₃ nano cubes by the hydrothermal method with ammonia mineralizer.