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首页> 外文期刊>Physica, B. Condensed Matter >Electric, dielectric and optical studies of the lower phase transition of lithium ammonium sulphate single crystals
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Electric, dielectric and optical studies of the lower phase transition of lithium ammonium sulphate single crystals

机译：硫酸铵锂单晶低相变的电学，介电和光学研究

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The dielectric permittivity (#epsilon#) and the dc electrical resistivity (#rho#) of pure LiNH_4SO_4 (LAS) single crystals have been measured in the temperature range 230-350 K including the lower phase transition at about 283 K. Anomalous behaviours before and at the transition point were observed. The temperature dependence of #rho# yielded #DELTA#E = 0.11 and 0.91 eV for the energy activating the charge transport mechanisms before and after the transition. A "pre-transition" phenomena was observed while measuring both #rho# and #epsilon#. The optical transmittance at different temperatures was also measured and hence the absorption coefficient (#alpha#) and optical band gap E_g~(opt.) were deduced. The validity of Urbach's rule was checked and hence the steepness parameter #sigma# and the exciton energy E_0 were calculated at different temperatures. #rho#, #epsilon#, #alpha# and E_g~(opt.) for LAS crystals doped with 5% Co~(2+) or Cu~(2+) were also measured and they were compared with the results of the pure crystals.
机译：纯LiNH_4SO_4（LAS）单晶的介电常数（＃epsilon＃）和直流电阻率（＃rho＃）已在230-350 K的温度范围内进行了测量，包括在283 K处的较低相变。并且在过渡点被观察到。 ＃rho＃的温度依赖性产生＃DELTA＃E = 0.11和0.91 eV，用于能量在跃迁之前和之后激活电荷传输机制。在同时测量＃rho＃和＃epsilon＃时观察到“过渡前”现象。还测量了在不同温度下的透光率，因此推导了吸收系数（＃α＃）和光学带隙E_g〜（opt。）。检查了Urbach规则的有效性，因此计算了不同温度下的陡度参数＃sigma＃和激子能量E_0。还测量了掺杂5％Co〜（2+）或Cu〜（2+）的LAS晶体的#rho＃，＃epsilon＃，＃alpha＃和E_g〜（opt。），并将其与纯净的晶体。

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