Slow-structural relaxation in the metal–nonmetal transition range of liquid mercury: I. Experimental evidence
Slow-structural relaxation in the metal–nonmetal transition range of liquid mercury: I. Experimental evidence
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液态汞金属-非金属转变范围内的缓慢结构弛豫：一、实验证据
DOI：
10.1088/0953-8984/13/46/303
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
M. Yao
中科院分区：
文献类型：
--
作者：
H. Kohno;M. Yao
本文用超声脉冲回波法在20、32和44 MHz频率下测量了膨胀液汞在1600 ℃和210 MPa的温度和压力范围内的吸声系数α。除了临界衰减外，我们还观察到α/f2密度依赖性在9 g cm−3附近的次极大值，在那里发生了金属-非金属（M-NM）跃迁。随着频率的增加，α/f2的次极大值有减小的趋势，说明在液态汞的M-NM跃迁区发生了某种弛豫过程.利用M-NM过渡区中的临界衰减和反常衰减随频率变化的差异，将观测到的声衰减分离为临界衰减和反常衰减。假设由M-NM跃迁引起的弛豫过程为Debye型弛豫模型，我们估计了弛豫时间τ和弛豫的相对强度βr/β0 <$（β0 − β∞）/β0，其中β0和β∞分别是低频和高频极限下的绝热压缩系数。由此产生的τ约为2 ns，几乎与密度无关。另一方面，βr/β0取决于密度，在8.5 g cm−3附近有一个宽的最大值（~4%）。
The sound absorption coefficient, α, of expanded liquid mercury has been measured by means of the ultrasonic pulse-echo method at 20, 32 and 44 MHz in the temperature and pressure range up to 1600 °C and 210 MPa. Besides the critical attenuation, we have observed the secondary maximum in the density dependence of α/f2 around 9 g cm−3, where the metal–nonmetal (M–NM) transition occurs. When the frequency increases, the secondary maximum of α/f2 tends to be smaller, which suggests that some kind of relaxation process takes place in the M–NM transition range of liquid mercury. We have separated the observed sound attenuation into the critical attenuation and the anomalous attenuation in the M–NM transition region utilizing the difference of the frequency dependence between the two components. Assuming a Debye-type relaxation model for the relaxation process due to the M–NM transition, we have estimated the relaxation time, τ, and the relative strength of the relaxation, βr/β0 ≡ (β0 − β∞)/β0, where β0 and β∞ are the adiabatic compressibility in the low-frequency and the high-frequency limit, respectively. The resultant τ is about 2 ns and almost independent of density. On the other hand, βr/β0 depends on density and has a broad maximum (~4%) around 8.5 g cm−3.