The tribological behaviors of graphene and graphene oxide (GO) as water-based lubricant additives were evaluated by use of a reciprocating ball-on-plate tribometer for magnesium alloy-steel contacts. Three sets of test conditions were examined to investigate the effect of concentration, the capacity of carrying load and the endurance of the lubrication film, respectively. The results showed that the tribological behaviors of water can be improved by adding the appropriate graphene or GO. Compared with pure deionized water, 0.5 wt.% graphene nanofluids can offer reduction of friction coefficient by 21.9% and reduction of wear rate by 13.5%. Meanwhile, 0.5 wt.% GO nanofluids were found to reduce the friction coefficient and wear rate up to 77.5% and 90%, respectively. Besides this, the positive effect of the GO nanofluids was also more pronounced in terms of the load-carrying capacity and the lubrication film endurance. The wear mechanisms have been tentatively proposed according to the observation of the worn surfaces by field emission scanning electron microscope-energy dispersive spectrometer (FESEM-EDS) and Raman spectrum as well as the wettability of the nanofluids on the magnesium alloy surface by goniometer.

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2Controlling functionalities, such as magnetism or ferroelectricity, by means of oxygen vacancies (VO) is a key issue for the future development of transition metal oxides.Progress in this field is currently addressed through VO variations and their impact on mainly one order parameter. Here we reveal a new mechanism for tuning both magnetism and ferroelectricity simultaneously by using VO. Combined experimental and density-functional theory studies of Eu0.5Ba0.5TiO3-δ, we demonstrate that oxygen vacancies create Ti 3+ 3d 1 defect states, mediating the ferromagnetic coupling between the localized Eu 4f 7 spins, and increase an off-center displacement of Ti ions, enhancing the ferroelectric Curie temperature. The dual function of Ti sites also promises a magnetoelectric coupling in the Eu0.5Ba0.5TiO3-δ. 3 Transition metal oxides (TMOs) are attracting significant attention due to their astonishing variety of technologically important physical properties, such as two-dimensional electron gas (2DEG), colossal magnetoresistance (CMR), and multiferroic behavior, etc [1][2][3]. Tuning the concentration and distribution of ions and vacancies in TMOs provides a route to create and control new functionalities [4]. For many applications, for better or worse, the functionality of TMOs and thin film devices is strongly affected by the formation and distribution of oxygen vacancies (VO). For instance, the introduction of VO causes a displacement of the Fe ions in (LaFeO3)2/(SrFeO3) superlattices, which induces the polar order [5]. VO also enable room-temperature ferroelectricity in SrTiO3 thin films by manipulating the TiO6 octahedral tilting around the vacancy site [6]. The electronic properties of these TMOs, especially ABO3-pervoskite structure, are extremely sensitive to structural distortions consisting of cation displacements, deformations, and rotations in an ideal three-dimensional framework of corner-connected BO6 octahedra [7,8]. On the other hand, VO are well known to play a pivotal role in magnetic properties. Biškup et al.suggested that ordered VO are responsible for insulating ferromagnetism in strained epitaxial LaCoO3-δ films [9]. Similarly, magnetic phenomena were observed at the SrTiO3/LaAlO3 interface [10,11] and oxygen-deficient bulk SrTiO3-δ crystals [12].Previous studies have shown that it is possible to manipulate the functionality of TMO materials by controlling one order parameter at a time through the concentration or spatial distribution of VO. A natural question arises whether a single experimental parameter, VO, has the ability to simultaneously control multiple order parameters, 4 such as both magnetism and ferroelectricity. In particular, multiferroics with ferromagnetic-ferroelectric (FM-FE) coupling are highly promising for fundamental research and practical applications [13][14][15]. They are scarce, however, due to the near-incompatibility of the formation of magnetic order (partial filled d-orbitals in 3d TMOs) and the conventional off-centering mechanism of ferroelectricity (empty d-orbital...