Xu Guang Zheng

LiNbO3:Pr3+: A Multipiezo Material with Simultaneous Piezoelectricity and Sensitive Piezoluminescence

Red-emitting piezoluminescence (elasticoluminescence) is achieved by doping rare earth Pr3+ into the well-known piezoelectric matrix, LiNbO3 . By precisely tuning the Li/Nb ratio in nonstoichiometric Li x NbO3 :Pr3+ , a material that exhibits an unusually high piezoluminescence intensity, which far exceeds that of any well-known piezoelectric material, is produced. Li x NbO3 :Pr3+ shows excellent strain sensitivity at the lowest strain level, with no threshold for stress sensing. These multipiezo properties of sensitive piezoluminescence in a piezoelectric matrix are ideal for microstress sensing, damage diagnosis, electro-mechano-optical energy conversion, and multifunctional control in optoelectronics.

Raman spectroscopic study of the frustrated spin 1/2 antiferromagnet clinoatacamite.

Raman spectroscopy is a valuable and complementary tool for studying geometrically frustrated magnetic systems due to the intrinsic spin-phonon coupling. Here, we report on a Raman spectroscopic study of the geometrically frustrated spin 1/2 antiferromagnet microcrystalline clinoatacamite Cu2(OH)3Cl, focusing on the anomalous transition into the intermediate phase at T(c1) = 18.1 K. By measuring the temperature-dependent (295-4 K) full spectral profiles and main representative modes in spectral regions from 4000 to 95 cm(-1), we observed probable signatures of successive magnetic transitions near T(c1) = 18 K and T(c2) = 6.4 K in the Raman band frequencies and peak widths of the representative modes. Further, we observed a pronounced Raman spectroscopy background featuring a broad continuum at all temperatures. A quantitative analysis reveals that spin fluctuations may exist on a picosecond time scale in the intermediate phase. The short time scale falls out of the μSR time window; therefore, in the intermediate phase, the μSR study as reported in (2005 Phys. Rev. Lett. 95 057201) apparently only probed the local field of the ordered spins but overlooked the quickly fluctuating ones. This is likely to give a reasonable explanation of the fact that only a small entropy release occurs at T(c1) = 18 K although a long-range order is formed.

Mid-IR and Raman Spectral Properties of Clinoatacamite-Structure Basic Copper Chlorides

Basic copper chloride Cu2(OH)3Cl and Cu2(OD)3Cl polycrystalline sample were successfully synthesized in the same single phase of clinoatacamite-structure, and the latter’s mid-infrared absorption spectra (4000-400cm–1) and Raman spectra (4000-95cm–1) were first, to the best of our knowledge, measured respectively by FTIR spectroscopy and Micro-Raman spectroscopy to study the corresponding relationship between their spectral properties and crystal structure. Through the comparative analysis of the four spectra we definitely assign or tentatively suggest the vibration modes of OH/D groups in the trimeric hydrogen bond environment, (H/DO)–Cu–(OH/D), Cl–Cu–Cl. These results can be propitious to their low temperature spectral properties which must help to understand the underlying physics of their exotic geometric frustration phenomenon.

Deuterium ordering found in new ferroelectric compound Co2(OD)3Cl

A detailed temperature-dependent Raman spectroscopic study revealed a new type of deuterium-order ferroelectrics in a geometrically frustrated magnet Co2(OD)3Cl at T = 229 K. Significant changes in the parameters of the Raman vibration modes were observed near T, suggesting a strong phonon-charge coupling. Additional asymmetric phonon bands appeared below around T, which are consistently interpreted by phonon folding processes due to a small local structural change resulting from the ordering of deuterium. The wavenumber and intensity changes of the Raman-active modes, as well as the normalized intensities of the additional bands, all follow a power-law fit Δω, ΔI, I ∝ (1 − T/TC)2β, wherein TC = 230 K ~ T and β = 0.35(2), clearly demonstrating an ordering process below T. The critical exponent is reminiscent of a second order transition. Our study presents a rare and new type of multiferroic material with ferroelectricity arising from the deuterium ordering in geometrically frustrated magnets.

Mid-IR and Raman Spectral Properties of Geometrically Frustrated Atacamite Hydroxyl Copper Chloride

The mid-IR and Raman spectra of geometrically frustrated atacamite hydroxyl copper chloride are measured by FTIR spectroscopy and HR800 Raman spectroscopy, respectively. The microscopic origins of bands within the functional group and the fingerprint regions are suggested by the known crystal structure parameters. Five distinct regions involved in hydroxyl stretching, overtones, hydroxyl deformation, Cu-O stretching, O–Cu–O symmetric stretching and O–Cu–O bending modes, pyramid-structure Cl≡Cu3 vibration modes, lattice modes, respectively.

Utilizing muon-spin-relaxation to probe ferroelectric transition in hydroxyl salt Co2(OD)3Cl

ABSTRACT The muon spin relaxation (μSR), which uses spin-polarized muons to probe tiny local field in matters, is a useful tool for studying spin-related phenomena in magnets, superconductors and semiconductors, etc. Here we report a first successful application to ferroelectrics. We utilized μSR to detect a ferroelectric transition in a newly-identified ferroelectric material Co2(OD)3Cl. The deuteriums in Co2(OD)3Cl were found to be rapidly fluctuating in the paraelectric phase at high temperatures, then they drastically slowed down toward the ferroelectric transition at = 229 K, and eventually became quasi-static at around 160 K. Our study reveals that Co2(OD)3Cl is a deuterium-order ferroelectric material, and detailed analysis suggests that it can be viewed as new type of multiferroic material. The present study demonstrates that the conventional μSR can be an effective and powerful tool for ferroelectrics study.

Investigation of the Multiferroic Transition in CuO Single Crystal using Dielectric and Raman Spectroscopy Measurements

Single Crystal using Dielectric and Raman Spectroscopy Measurements Dongdong MENG, Xu-Guang ZHENG, Xingliang XU, Jun NAKAUCHI, Masayoshi FUJIHALA, Xiaodong LIU, Qixin GUO, Makoto MAKI 1 Department of Physics, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan 2 Department of Physics, Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan Department of Physics, College of Science, Tianjin Polytechnic University, Tianjin 300387, China Synchrotron Light Application Center & Department of Electrical and Electronic Engineering, Saga University, Saga 840-8502, Japan

More than Four Subtypes of Trimeric Hydrogen Bonds in Hydroxyl Halides

Through ten years physical investigation on the geometrically frustrated coordination compound series basic (hydroxyl and deuteroxyl) transition-metal halides M2(OH/D)3X (M=Mn, Fe, Co, Ni and Cu; X=Cl, Br and I), we have determined the existence of four crystal structures, whose space groups belong to Nos. 11, 14, 62 and 166, respectively, in this series till now. After studying their Raman spectra, we firmly believe that a nonnegligible hydrogen bond (H-bond) exists in every material. Considering carefully their local lattice environments of the basic groups, we find a new kind, to the best of our knowledge, of H-bond [(OH)3···M] and nominate it as the trimeric H-bond, and further confirm three types of symmetric structures, which have totally four subtypes of trimeric H-bonds so far. More two subtypes are predicted to exist in nature. This result may provide a new interesting subject for quantum chemists and material physicists.

Low Temperature Raman Spectroscopic Study on γ-Cu2(OH)3Cl

The low temperature (T) Raman spectroscopic study on the geometrically frustrated clinoatacamite γ-Cu2(OH)3Cl is reported. By measuring the T-dependent spectral profiles and representative modes, we have obtained auxiliary evidence of successive magnetic transitions near Tc1 =18.1 K and Tc2 =6.4 K determined accurately by the magnetic experiments in the Raman band frequencies and peak widths of the representative modes for magnetic research conclusions and observed a pronounced Raman spectroscopy background featuring a broad continuum at all Ts. A quantitative analysis reveals spin fluctuations on a picosecond time scale in the intermediate phase.

Spectral Properties of Alpha-Cu2(OH/D)3Br at Room Temperature

The newly identified magnetic geometric frustration material-botallackite-structure deuteroxyl copper bromide α-Cu2(OD)3Br sample was successfully synthesized in the same single phase (polycrystalline) as the H-isotope substituted sample of α-Cu2(OH)3Br, and its IR (4000-400 cm–1) absorption and Raman (4000-95 cm–1) spectra at room temperature are first, to the best of our knowledge, measured to study the corresponding relationship between these iso-structural compounds. Through the comparative analysis with those of α-Cu2(OH)3Br reported previously, we definitely assign or tentatively suggest their vibration modes according to the result of the factor group analysis.