SUCCESSIVE PHASE TRANSITION OF HEXAGONAL TYPE BARIUM TITANATE

六方型钛酸钡的连续相变

• 批准号: 03640314
• 负责人: AKISHIGE Yukikuni
• 金额: $ 1.09万
• 依托单位: UNIVERSITY OF SHIMANE
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1991
• 资助国家: 日本
• 起止时间: 1991 至 1992
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03640314/
• 关键词: BARIUM TITANATE; RAMAN SCATTERING; FERROELECTRICITY; FERROELASTICITY; SOFT-MODE; DIELECTRIC CONSTANT; SPECIFIC HEAT; STRUCTURAL PHASE TRANSITION; ソフト・モ-ド

Hexagonal modification of barium titanate exhibits successive phase transition at To=222K and Tc=74K, and below Tc a ferroelectric activity occurs. In order to elucidate the mechanism of the phase transition, we have made dielectric, specific heat and Raman scattering measurements. Following results are obtained. 1.Dielectric properties under hydrostatic pressures : The dielectric constants along the c-axis of the single crystal were investigated as functions of hydrostatic pressure to 8kbar and temperature from 5K to 300K. The transition point To (222K at 1 bar) decreases linearly with increasing pressure at a rate -3.0K/kbar and no significant difference is observed in the shape of the dielectric anomaly at To. While, the dielectric constant at around Tc decreases apparently with increasing pressure and at ca. 10kbar the anomaly at Tc disappears. The pressure derivative of Tc is about -0.7K/kbar. 2. Specific heat : The specific heat of the polycrystalline sample was measured using a high-precision adiabatic calorimeter over the temperature range from 5K to 300K. The specific heat vs T curve shows a typical second-order type anomaly at To. However, the specific heat anomaly associated with the ferroelectric phase transition at Tc has not been detected. 3. Polarized Raman scattering : In order to closely investigate the behavior of the Raman spectra at around Tc, we have made the polarized Raman scattering measurement using thin a- and b-plate samples (ca. 0.3mm thick). In the ferroelectric phase below Tc, existence of an additional phonon mode at 57cm^<-1> has been confirmed ; this line appears below Tc only in the zz polarization and the intensity of the mode behaves like an order-parameter. No additional soft-optic mode was observed at Tc ; however, only the lower frequency mode of two soft modes existing below To shows anomalous behaviors at around Tc.

在Tc = 222 K和Tc= 74 K时，钛酸钡的相转变是连续的，在低于Tc时出现铁电活性。为了阐明相变的机制，我们进行了介电，比热和拉曼散射测量。获得了以下结果。1.在静水压力下的介电性能：研究了单晶c轴方向沿着的介电常数随静水压力至8 kbar和温度从5 K至300 K的变化。转变点T0（222 K，1bar）随压力的增加以-3.0K/kbar的速率线性下降，在T0处的介电异常形状没有明显的差异。而在Tc附近，介电常数随压力的增加而明显减小，在ca. 10 kbar时Tc处的异常消失。Tc的压力导数约为-0.7K/kbar。2.比热：用高精度绝热量热计测量了多晶样品在5 ~ 300 K温度范围内的比热。比热-T曲线在T_o处呈现典型的二级异常。然而，与铁电相变在Tc的比热异常尚未被检测到。3.偏振拉曼散射：为了仔细研究在Tc附近的拉曼光谱的行为，我们使用薄的a-和b-板样品（约100 μ m）进行了偏振拉曼散射测量。0.3mm厚）。在低于Tc的铁电相中，已经证实了在57 cm ^处存在额外的声子模式<-1>;该线仅在zz极化中出现在Tc以下，并且模式的强度表现得像序参数。没有额外的软光学模式，观察到在Tc，然而，只有较低的频率模式的两个软模式下存在的到显示异常行为在Tc附近。

项目成果

Y.AKISHIGE,J.NAKAHARA,E.SAWAGUCHI: "Hydrostatic Pressure Effects on the Raman Scattering in Hexagonal BaTio3" J.Phys.Soc.Jpn.60. 1115-1122 (1991)

Y.AKISHIGE、J.NAKAHARA、E.SAWAGUCHI：“静水压力对六方 BaTio3 中拉曼散射的影响”J.Phys.Soc.Jpn.60。

Y.AKISHIGE and K.OHI: "Low Frequency Dielectric Dispersion in Sr_2Ta_2O_7" J.Phys.Soc.Jpn.vol. 61. 1351-1356 (1992)

Y.AKISHIGE 和 K.OHI：“Sr_2Ta_2O_7 中的低频介电色散”J.Phys.Soc.Jpn.vol。

Y.AKISHIGE and Y.KAMISHINA: "Effects of Electric Fields on the Dielectric Constants in(Rochelle Salt)_<1-X>(Ammonium Rochelle Salt+)x Mixes Gystals with 0∠__-X∠__-0.025" J.Phys.Soc.Jpn.61. 4589-4595 (1992)

Y.AKISHIGE 和 Y.KAMISHINA：“电场对（罗谢尔盐）_<1-X>（罗谢尔铵盐+）x 与 0∠__-X∠__-0.025 混合 Gystals 介电常数的影响”J.Phys .Soc.Jpn.61。4589-4595 (1992)

Y.Akishige H.Takahashi and N.Mori: "Effects of Hydrostatic Pressures on the Dielectric Properties of Ferroelectric Hexagonal BaTiO_3"

Y.Akishige H.Takahashi 和 N.Mori：“静水压力对铁电六方 BaTiO_3 介电性能的影响”

Y.AKISHIGE and K.OHI: "Low Freguency Dielectric Dispersion in Sr_2Ta_2O_7" J.Phys.Soc.Jpa.61. 1351-1356 (1992)

Y.AKISHIGE 和 K.OHI：“Sr_2Ta_2O_7 中的低频介电色散”J.Phys.Soc.Jpa.61。