Universal relation between oxygen mass and Tc in SrTiO3
Universal relation between oxygen mass and Tc in SrTiO3
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SrTiO3 中氧质量与 Tc 之间的普遍关系
DOI：
10.1143/jpsj.72.1310
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发表时间：
2003
影响因子：
1.7
通讯作者：
Ruiping Wang
中科院分区：
文献类型：
--
作者：
M. Itoh;Ruiping Wang
最近我们对SrTiO_3（STO）中~（18）O取代~（16）O的研究表明，~（18）O取代的STO（STO_（18））具有铁电性，其Tc ~（2）由Tc% Δ Tc ~（x）= 2，3，4）给出，其中x为同位素的取代分数，xc为临界分数。然而，在Tc附近的拖尾的介电峰、介电常数”0“的真实的部分的大幅度依赖性、”0“的大的偏压依赖性以及在Tc以下极化随时间的弛豫表明STO 18远不是典型的铁电体。4-6)虽然最近我们的数据表明，STO 18经历了一个无规场（RF）挫折铁电转变低于25 K，RF的起源还没有得到澄清。本文通过比较16 O-18 O和16 O-17 O-18 O两种氧同位素混合体系在STO中的介电性质，来阐明：（1）氧的质量是否是决定氧同位素交换STO铁电相变温度Tc的唯一参数;（2）氧原子的随机混合是否对Tc有影响。根据先前报道的方法制备样品。4)在本研究中，一个额外的样品的双氧同位素系统，SrTi（16 O 0：01 18 O 0：99）3（STO 18 -99），准备完成的Tc与x关系SrTi（16 O 1x 18 Ox）3（STO 18 - 100 x）。由于商业上可获得的18 O气体的最高纯度为99%，因此STO 18 -99是使用本制备方法可获得的具有最高18 O交换率的样品。对于17 O的交换，使用组成为16 O 38.5%、17 O 58.2%和18 O 3.3%的氧气（Isotech Co.）用了使用两块尺寸为7 2 0：3 mm 3的（110）c面SrTiO 3板进行氧同位素交换。将SrTiO 3板在氧气中加热700小时，然后称重。质量增量与完全交换的预期值一致，为1.06%。因此，样品的组成为16 O 38.5%、17 O 58.2%和18 O 3.3%（STO 18 -3/17-58）。将这样交换的样品之一在16 O2 - 18 O2混合气体中再进行700小时的交换，以获得目标组成：16 O 28.5%、17 O 43.1%和18 O 28.5%（STO 18 -28/17-43）。两个样品的平均氧原子质量分别为16.65（STO 18 -3/17-58）和17.00（STO 18 -28/17-43）。为了避免非线性响应，使用HP 4182 A LCR计，使用40 V/m的低ac测试信号测量复介电常数（“0 Ω i”00）。
Recent our studies on 18O substitution for 16O in SrTiO3 (STO) revealed that 18O-substituted STO (STO18) shows a ferroelectricity1) whose Tc 2) is given by Tc% Aðx Ā xcÞ1= 2, 3, 4) where x is the substituted fraction of the isotope and xc the critical fraction. However, smeared dielectric peak around Tc, large amplitude dependence of real part of dielectric constant" 0, large bias dependence of" 0, and relaxation of polarization with time below Tc suggest the STO18 is far from typical ferroelectric. 4–6) Although recent our data suggest that STO18 undergoes a random-field (RF) frustrated ferroelectric transition below 25K, the origin of RFs has not been clarified. 7, 8) In the present note, we try to compare the dielectric properties of two mixed oxygen isotope systems 16O–18O and 16O–17O–18O in STO to clarify that (1) whether the mass of oxygen is the only parameter determining the ferroelectric phase transition temperature Tc of the oxygen isotope exchanged STO, and (2) whether or not the random mixing of oxygen atoms has any effect on Tc’s. Samples were prepared according to the method previously reported. 4) In the present study, one additional sample of the two-oxygen-isotope system, SrTi (16O0: 01 18O0: 99) 3 (STO18-99), was prepared for the completion of the Tc vs x relation of SrTi (16O1Āx 18Ox) 3 (STO18-100x). Because the highest purity of commercially obtainable 18O gas is 99%, STO18-99 is the sample with the highest 18O exchange rate available using the present preparing method. For the exchange of 17O, oxygen gas with a composition of 16O 38.5%, 17O 58.2%, and 18O 3.3%(Isotech Co.) was used. Two plates of (110) c-faced SrTiO3 of 7 Â 2 Â 0: 3 mm3 size were used for the oxygen isotope exchange. The SrTiO3 plates were heated in the oxygen gas for 700 hours, and then weighed. Mass increment was in good agreement with that of the expected value for the full exchange, þ1: 06%. Thus the samples are of the composition of 16O 38.5%, 17O 58.2%, and 18O 3.3%(STO18-3/17-58). One of the thus exchanged samples was subjected to further exchange in 16O2–18O2 mixed gas for another 700 hours to attain the aimed composition: 16O 28.5%, 17O 43.1%, and 18O 28.5%(STO18-28/17-43). The average oxygen atomic masses of the two samples are 16.65 for STO18-3/17-58 and 17.00 for STO18-28/17-43, respectively. To avoid nonlinear response, complex dielectric constant (" 0 Ā i" 00) was measured using a low ac test signal, 40V/m, using HP 4182A LCR meter.