Li Guo-Rong

Nanoscale Thermal Response in ZnO Varistors by Atomic Force Microscopy

We report the application of customer-built scanning thermal microscopy (SThM) based on a commercial atomic force microscope to investigate local thermal inhomogeneity of ZnO varistors. The so-called 3ω method, generally used for measuring macroscale thermal conductivity, is set up and integrated with an atomic force microscope to probe the nanoscale thermal property. Remarkably, thermal contrasts of ZnO varistors are firstly imaged by the SThM, indicating the uniform distribution of spinel phases at triple points. The frequency-dependent thermal signal of ZnO varistors is also studied to present quantitative evaluation of local thermal conductivity of the sample.

Reorientation of Defect Dipoles in Ferroelectric Ceramics

We investigate the frequency, temperature, tetragonality and quenched temperature dependences of the hysteresis loops in Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 (PMnN-PZT) ceramics. It has been demonstrated that the polarization-field hysteresis curves show ``pinched shapes when tested at room temperature, higher frequency or using the large-tetragonality specimen. While normal square-like loops are observed at 200°C and 0.01 Hz or using the small-tetragonality one. Meanwhile, close relations between the P–E loops and the applied frequency, temperature or tetragonality reveal that there exists a typical relaxation time corresponding to the reorientation of the defect dipoles. It can be seen further from the quenched temperature dependences of the loops that the reorientation of the defect dipoles may influence the pinching. Compared to the intrinsic depinning procedure induced by changes of the distribution of defect dipoles, we provide new evidence for extrinsic depinning mechanism of the defect dipoles in the ferroelectric ceramics.

Local Piezoresponse and Thermal Behavior of Ferroelastic Domains in Multiferroic BiFeO3 Thin Films by Scanning Piezo-Thermal Microscopy

A dual probe, i.e., high resolution scanning piezo-thermal microscopy, is developed and employed to characterize the local piezoresponse and thermal behaviors of ferroelastic domains in multiferroic BiFeO3 thin films. Highly inhomogeneous piezoelectric responses are found in the thin film. A remarkably local thermal transformation across ferroelastic domain walls is clearly demonstrated by the quantitative 3ω signals related to thermal conductivity. Different polarization oriented ferroelastic domains are found to exhibit different local thermal responses. The underlying mechanism is possibly associated with the inhomogeneous stress distribution across the ferroelastic domain walls, leading to different phonons scattering contributions in the BiFeO3 thin film.

Potential Barrier Behavior of BaTiO3—(Bi0.5Na0.5)TiO3 Positive Temperature Coefficient of Resistivity Ceramic*

High-Curie-temperature (Tc) lead-free Y-doped 90 mol%BaTiO3—10 mol%(Bi0.5Na0.5)TiO3 ceramic with positive temperature coefficient of resistivity (PTCR) is prepared by the conventional solid state reaction in nitrogen atmosphere. The PTCR ceramic exhibits a room-temperature resistivity (ρ25) of ~500Ωcm and a high PTCR effect (maximum resistivity (ρmax)/minimum resistivity (ρmin)) of ~4.5 orders of magnitude. A capacitance-voltage approach is first employed to calculate the potential barrier (Φ) of the grain boundary of PTCR ceramic above Tc. It is found that the potential barrier changes from 0.17 to 0.77 eV as the temperature increases from 180 to 220°C, which is very close to the predictions of the Heywang–Jonker model, suggesting that the capacitance-voltage method is valid to estimate the potential barrier of PTCR thermistor ceramics.

Piezoresponse Force Microscopy Imaging of Ferroelectric Domains in Bi(Zn1/2Ti1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Piezoelectric Ceramics

Bismuth zinc titanate dopied lead magnesium niobate-lead titanate[Bi(Zn1/2Ti1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3(BZT-PMN-PT)] piezoelectric ceramics are synthesized by the conventional solid state reaction method. Ferroelectric domain structures and the evolutionary behavior of BZT-PMN-PT ceramics under an external in-plane electric field are investigated by piezoresponse force microscopy (PFM). It is found that the BZT doping has a significant effect on the domain configurations and the domain kinetic behavior of the piezoelectric BZT-PMN-PT solid solution ceramics. Microdomains embedded in the macrodomains, induced by the BZT dopant in the solid solution ceramics, are clearly observed by PFM and their volume increases with increasing amounts of BZT doping. The microdomains of BZT-PMN-PT piezoelectric ceramics exhibit better domain dynamic behavior stability than macrodomains under an external in-plane electric field.

The Observation of Martensite and Magnetic Domain Structures in Ni53Mn24Ga23 Shape Memory Alloys by Scanning Electron Acoustic Microscopy and Scanning Thermal Microscopy

We present observations of martensite variants and ferromagnetic domain structures of Ni53Mn24Ga23 ferromagnetic shape memory alloys with a pure tetragonal martensitic phase by using scanning electron acoustic microscopy (SEAM) and scanning thermal microscopy (SThM). Electron acoustic images show a polycrystalline morphology with martensite variants. Direct coincidence between crystallographic martensitic twin variants and magnetic domains is found. A domain-like structure, obtained by SThM, is firstly reported, and then confirmed by magnetic force microscopy (MFM). The experimental results will be helpful for investigating the local thermal properties of ferromagnets and understanding the relationship between martensite variants and magnetic domains.

高居里温度BaTiO 3 -(Bi 0.5 Na 0.5 )TiO 3 无铅正温度系数电阻陶瓷的制备

用传统的固相反应烧结法制备了(1– x mol%)BaTiO3-xmol%(Bi0.5Na0.5)TiO3(BBNTx)高温无铅正温度系数电阻( positive temperature coefficient of resistivity, PTCR)陶瓷。X射线衍射表明所有的BBNT x 陶瓷形成了单一的四方钙钛矿结构。SEM分析结果显示随着BNT含量的增加, 陶瓷晶粒尺寸减小。空气中烧结的0.2mol% Nb掺杂的BBNT1陶瓷, 室温电阻率为~10 2 Ω·cm, 电阻突跳为~4.5个数量级, 居里温度为~150℃。氮气中烧结的0.3mol% Nb掺杂的BBNTx(10≤x≤60)陶瓷, 同样具有明显的PTCR效应, 居里温度在180~235℃之间。随着BNT含量的增加, 材料的室温电阻率增大, 同时陶瓷的电阻突跳比下降。用传统的固相反应烧结法制备了(1– x mol%)BaTiO3-xmol%(Bi0.5Na0.5)TiO3(BBNTx)高温无铅正温度系数电阻( positive temperature coefficient of resistivity, PTCR)陶瓷。X射线衍射表明所有的BBNT x 陶瓷形成了单一的四方钙钛矿结构。SEM分析结果显示随着BNT含量的增加, 陶瓷晶粒尺寸减小。空气中烧结的0.2mol% Nb掺杂的BBNT1陶瓷, 室温电阻率为~10 2 Ω·cm, 电阻突跳为~4.5个数量级, 居里温度为~150℃。氮气中烧结的0.3mol% Nb掺杂的BBNTx(10≤x≤60)陶瓷, 同样具有明显的PTCR效应, 居里温度在180~235℃之间。随着BNT含量的增加, 材料的室温电阻率增大, 同时陶瓷的电阻突跳比下降。

An Alternating-Current Voltage Modulated Thermal Probe Technique for Local Seebeck Coefficient Characterization

An ac voltage-modulated thermal probe technique based on the atomic force microscope is developed to measure local Seebeck coefficients (S) of thermoelectric bulk and films. The characterization principle is based on the strictly quadratic relationship between the excited local dc Seebeck voltage and the applied ac voltage at high frequency. Excellent agreement is found between local S values and their corresponding macro-S values of thermoelectric bulk and thin films. This thermoelectric probe technique provides a very convenient, promising tool for local thermoelectric parameters with sub-micrometer scale resolution.

Sb掺杂Li 7 La 3 Zr 2 O 12 陶瓷的显微结构及离子导电性能研究

The garnet-related oxides Li7-xLa3Zr2-xSbxO12 (x = 0, 0.075) were prepared by solid-state reaction method. Crystal structure, microstructure, conductivity, and element distribution were characterized for the pure and Sb-doped Li7La3Zr2O12. Ionic conductivity of the Li7La3Zr2O12 is enhanced by Sb doping. An amorphous Li-La-Zr-Al-O thin film which is formed on the grain boundary of Sb-doped samples not only suppresses the abnormal grain growth but also eliminates the pores on the grain boundary. The ionic conductivity of Sb doped Li7-xLa3Zr2-xSbxO12 ceramic with x = 0.075 sintered at 1160°C reaches about 3.40×10 S/cm.采用传统固相反应法制备了锑掺杂的锆镧酸锂固体电解质陶瓷。对陶瓷的晶体结构、显微结构及元素分布、离子电导率进行了研究。结果表明: 少量锑掺杂可明显提高锆镧酸锂固体电解质陶瓷的离子电导率。1160℃烧结的锑掺杂固体电解质中, 晶粒表面形成无定型的薄膜。此薄膜抑制了晶粒生长, 消除了晶界上的气孔, 提高了陶瓷致密度, 提高了陶瓷的离子导电率。1160℃烧结得到的Li 6.925 La 3 Zr 1.925 Sb 0.075 O 12 陶瓷离子电导率高达3.40×10 -4 S/cm。采用传统固相反应法制备了锑掺杂的锆镧酸锂固体电解质陶瓷。对陶瓷的晶体结构、显微结构及元素分布、离子电导率进行了研究。结果表明: 少量锑掺杂可明显提高锆镧酸锂固体电解质陶瓷的离子电导率。1160℃烧结的锑掺杂固体电解质中, 晶粒表面形成无定型的薄膜。此薄膜抑制了晶粒生长, 消除了晶界上的气孔, 提高了陶瓷致密度, 提高了陶瓷的离子导电率。1160℃烧结得到的Li 6.925 La 3 Zr 1.925 Sb 0.075 O 12 陶瓷离子电导率高达3.40×10 -4 S/cm。

含铋层状结构陶瓷CaBi 2 Nb 2 O 9 的A位掺杂改性研究

利用固相反应法合成了Ca 1- x (KLa) x /2 Bi 2 Nb 2 O 9 ( x =0~0.20)( x KLaCBNO)铋层状陶瓷, 分析不同KLa掺杂量对CaBi 2 Nb 2 O 9 (CBNO)基陶瓷微观结构、介电、压电及电导性能的影响. XRD分析表明KLa的引入未改变CBNO陶瓷的单相结构. SEM和介电系数温度谱结果分别显示, KLa掺杂量的增加, 细化尺寸趋于一致, 而居里温度( T c )从943℃降低至875℃, 其峰值介电常数减小、峰值介电损耗增大. 当掺杂量 x =0.1时, 样品的高温电阻率较纯CBNO显著升高, 压电系数 d 33 由5.2 pC/N提高到15.8 pC/N, 居里温度高达870℃, 说明A位(KLa)掺杂改性后的CBNO陶瓷在高温传感器等领域具有潜在的应用前景.利用固相反应法合成了Ca 1- x (KLa) x /2 Bi 2 Nb 2 O 9 ( x =0~0.20)( x KLaCBNO)铋层状陶瓷, 分析不同KLa掺杂量对CaBi 2 Nb 2 O 9 (CBNO)基陶瓷微观结构、介电、压电及电导性能的影响. XRD分析表明KLa的引入未改变CBNO陶瓷的单相结构. SEM和介电系数温度谱结果分别显示, KLa掺杂量的增加, 细化尺寸趋于一致, 而居里温度( T c )从943℃降低至875℃, 其峰值介电常数减小、峰值介电损耗增大. 当掺杂量 x =0.1时, 样品的高温电阻率较纯CBNO显著升高, 压电系数 d 33 由5.2 pC/N提高到15.8 pC/N, 居里温度高达870℃, 说明A位(KLa)掺杂改性后的CBNO陶瓷在高温传感器等领域具有潜在的应用前景.