微晶玻璃中的声传播

本文把悬浮液中的声学处理方法应用到微晶玻璃中,导出了微晶玻璃中声速和声衰减系数随结晶度变化的表达式,并通过实验进行了证实。     

混晶（Rb_xK_（1－x））_2SnCl_6的相变研究

用非极性喇曼散射光谱研究了混晶（Ｒｂ_ｘＫ_（１－ｘ））_２ＳｎＣｌ_６性质随组份（０＜ｘ＜１）及温度（１０Ｋ＜Ｔ＜３００Ｋ）的变化。发现在纯Ｋ_２ＳｎＣｌ_６晶体中用Ｒｂ￣＋部分替代Ｋ￣＋后，将降低原Ｋ_２ＳｎＣｌ_６的相变温度Ｔｃｌ。当混晶中Ｒｂ￣＋成份超过极限浓度（ｘ＞０．７）后，该相变就被抑制。不同组份样品的同一喇曼模频率，随Ｒｂ￣＋的增加，向低频方向移动。用平均力常数拟合给出很好的理论解释。     

布里渊散射研究K_2SnCl_6晶体的弹性常数和声学模软化

本文测量了六卤素金属化合物六氯锡钾室温布里渊散射纵声速和横声速。计算了晶体的弹性常数、折射率、体积压缩系数。并进一步研究了[111]方向声子的纵声速随温度的变化关系,发现当温度从高温降到256K附近,C_(11)+2C_(12)发生突变。利用Pippard关系进行了分析,得出晶体在T=256K附近发生一级相变。这种声学反常行为可以用均匀弹性应变场与软模坐标涨落的非线性耦合来解释。     

STUDIES ON THE BEHAVIOR OF THE INTERNAL VIBRATIONAL MODES IN (NH4)2TexSn1-xCl6 MIXED CRYSTALS

The behavior of the internal lattice vibrational modes in (NH4)2TexSn1-xCl6 mixed crystals has been investigated by Raman scattering. All of the Raman-active [MX6]2- internal modes show two-mode property in the mixed crystals with compositions from x?=?0 to 1, and apart from the sample with x?=?0.5, their energy positions are composition-independent. Space group calculations including site symmetry considerations and frequency fittings describe a good force field model. It has been demonstrated that the composition-independent two-mode behavior may come from the strong clustering effect, rather than from the character of the gap and local modes of impurities in mixed crystals. For the sample with x?=?0.5, the two component elements seem to form a pseudo-periodic lattice structure.     

〔（NH_4）_xK_（1－x）〕_2SnCl_6混晶的喇曼散射研究

本文用喇曼散射的方法研究了六氯锡化钾铵混晶系列样品［（ＮＮ_４）_ｘＫ_（１－ｘ）］_２ＳｎＣｌ_５（ｘ＝０，０．０５，０．１，０．１５，０．２，０．２５，０，３，１）从室温到７７Ｋ的行为，首先观察到了其外振动模的双模行为，并且还发现了其一内模Ｔ_（２ｇｉｎｔ）的宽度随铵离子浓度ｘ的增加而增加，相变温度Ｔｃ却随铵离子浓度的增加而迅速下降，下降速率约为ｄＴ_ｃ／ｄｘ＝－６００Ｋ／ｍｏｌ，这一行为是由于正四面体的ＮＨ_４￣＋离子对正八面体的ＳｎＣｌ_６￣（２－）离子团的转动产生阻碍而引起。内模Ｔ_（２ｇｉｎｔ）的宽度变化也是由于铵离子的转动影响以及由它引起的晶格畸变所导致。双模行为来自于强烈的集团效应。     

RAMAN STUDIES ON THE PHASE TRANSITIONS OF (NH4)2SnBr6 CRYSTALS

We report here the structural phase transitions of the crystal (NH₄)₂SnBr₆ investigated by Raman scattering at temperatures ranging from 10K to room temperature. Two phase transitions occurring at 150 and ll0K are found. Based on the group theory, it is proposed that the crystal undergoes a second-order phase transition at 150 K, resulting from a ferro-distortion with symmetry Γ⁴⁺. The change of structure is confirmed to be O⁵_h to C⁵_4h, which is assigned to the rotary of [SnBr₆]^2- ion groups around the axis of <001>. Furthermore the crystal undergoes an order-disorder phase transition at ll0K which is related with the reorientation of the ammonium ion group. It is noticed that the change of the vibrational modes at 77K does not show any phase transition.     

RAMAN STUDIES ON THE PHASE TRANSITIONS OF (NH4)2SnBr6 CRYSTALS

We report here the structural phase transitions of the crystal (NH₄)₂SnBr₆ investigated by Raman scattering at temperatures ranging from 10K to room temperature. Two phase transitions occurring at 150 and ll0K are found. Based on the group theory, it is proposed that the crystal undergoes a second-order phase transition at 150 K, resulting from a ferro-distortion with symmetry Γ⁴⁺. The change of structure is confirmed to be O⁵_h to C⁵_4h, which is assigned to the rotary of [SnBr₆]^2- ion groups around the axis of <001>. Furthermore the crystal undergoes an order-disorder phase transition at ll0K which is related with the reorientation of the ammonium ion group. It is noticed that the change of the vibrational modes at 77K does not show any phase transition.     

Zerodur玻璃的晶化过程及其结构的研究

微晶化对提高玻璃态的机械强度,热稳定性和化学稳定性等性能有利。本文以Zerodur 玻璃为对象,采用自制系统与工艺,在不同热处理条件下,研究其晶化过程与晶化程度的关系,得到了最佳品化条件。并首先采用喇曼散射的频谱分析方法用于研究Zerodur 玻璃在不同晶化条件下徼晶结构的结晶度与晶粒度,计算结果与X 光测定结果能较好地符合。     

六氯铅铵晶体相变的拉曼散射研究

在５Ｋ～３００Ｋ温度范围内对六氯铅铵晶体进行了拉曼散射测量，该晶体在Ｔｃ＝７８Ｋ发生从立方结构（Ｏ＾５４）至三方结构（Ｃ＾２３ｉ）的二级相变，ＰｂＣｌ＾２－６八面体Ａ１ｇ模和ＮＨ＾＋４四面体Ａ１模的拉曼频移在Ｔｃ时出现极大值，八面体Ｔ２ｇ模，四面体Ｔ２模和外振动Ｔ２ｇ模在Ｔｃ以下发生连续分裂，另外在Ｔｃ以下观测到对应于高温相ＰｂＣｌ＾２－６八面体Ｔ１ｇ模的软模。