The discovery of high-temperature superconductivity (HTSC) in La2 − xSrxCuO4 by Müller [1] in 1986 marked a new era in the history of science. Soon, Wu et al. [2]. in 1987 discovered YBa2Cu3O7 (YBCO), which led to great achievements in all advanced fields of science and technology. However, still no consensus on a theoretical model to describe superconductivity (SC), the phase diagram (PD), and abnormalities in YBCO and other high-Tc cuprates, including the HTSC mechanism itself. In my former paper [3] studied SC in La2 − xSrxCuO4 (LBCO) using crystal symmetry effects on the distribution of Sr2 + atoms in the parent crystal, using the principles: (1) Crystal symmetry affects the distribution of Sr2 + dopants on lattice sites of the parent compound; (2) Sr2 + dopants affect lattice symmetry and SC. This gives a new vision for SC in LBCO and may be for other cuprates. For LBCO: 1-By a statistical method discovered that distances between doped LBCO crystals by O atoms equals coherence the length (CL) at the concentration of start of SC; 2- Using a model for the PD depending on distribution of (1 & 2 ) Sr2 + dopants ( leads to max Tc, adding more atoms decline it )for all the lattice sites each leads to represent a new phase in PD, thus succeed in explanations of the unclear changes in the phase diagram were obtained. Here in this research, the method is extended to study HTSC of YBa2Cu3O7.The compound YBCO is different in crystal structure and doping mechanism from LSCO, but the active element in both is the CuO layer, however the method with modifications leads to fruitful results includes:1- Determination of the correct theoretical value of the coherence length (CL) for YBCO by applying symmetry effects to find relation between the distance between doped YBCO crystals and corresponding hole concentration, for this task, two methods were designed i.e. statistical and the matrix methods, it was found ( by statistical method for YBCO, CL = 16.8 Å; by matrix method CL = 16.33 Å) these are in excellent agreement with experimental values when the hole concentration is ( 0.05), at which SC started; 2- Phase coherence will not started unless the distances between dopants is within the CL. So one of the lost fundamentals puzzles in HTSC in cuprates may be found, (may be the lost fundamental point that researchers seek )because CL is a basic concept in HTSC, linked with phase coherence which is the third and the control operation needed to start SC after charge parring and condensation ;3- This leads to understand that SC occurs in three stages: parring of charge carriers during hole doping instant, and condensation of charged pairs to low energy levels, and Phase coherence which occurs due to interaction between YBCO crystals doped with holes. 4- This leads to considering that the two stages, i.e., pairing of charge carriers and Phase coherence, are independent of each other and require different physical treatments, but they complement each other as one. This independence of the two stages i.e. paring of charge carriers, and Phase coherence may explain the difficulties in predicting(or explaining ) phase diagram of YBCO, whereas using the basic aspects of the new vision this research succeeded to a good extent to uncover and determine the role of symmetric distribution of dopants in explaining the complex behavior of phases in the phase diagram and, also the appearance of anomalies like charge strips. Therefore, this research constructed new models to explain the phase diagram and charged strips, as well as a suggested model for YBCO hole pairing. All the models are based on experimental facts and theoretical research. a- The phase diagram model PD: it introduced a new and original concept to explain the existence of the different phases in the PD as a result of doping with 1, 2, 3 up to 4 (O1) 1, 2, 3, 4 atoms on the O1 sites along the four b-coordinates in the basal planes in a certain sequence in YBCO crystal and, in the whole YBCO specimen happening under control of symmetry of YBCO parent crystal tell saturation at optimum Tc, addition of more O atoms leads to decline of Tc, all the process of symmetry effects, and the sequences of distribution of atoms was not considered in former models. The symmetry effects of YBCO also apply to LBCO, but here holes are introduced by doping with (1&2 )Sr2+ ions in the apexes of the central cube of the LBCO crystal. b-Charged strips (CS) model introduces an original concept for CS by phenomenological analysis of its structure and behaviors. Its abnormal nature and behavior represent a great problem and challenge for former models. Its detailed structure and nature were represented as a series of O-doped charged YBCO crystals. using a 4 × 4 pixel matrix of YBCO crystals, which represents the distribution of O1 atoms as a function of the a and b-axes, and their concentration P, also shows us the state of YBCO for a certain concentration. It is found that, at the concentration of the start of superconductivity, Pc, the distance between doped crystals is equal to the experimental value of the coherence length (CL). This new vision of the model for CS greatly enriched our understanding of SC in YBCO. c-The hole pairing model (HP): This research suggests a new model for Hole pairing (HP) in which the doped O atoms on the vacant O1 site attracts two lone d9 electrons from the sided Cu atoms and becomes O2− then, the negative space around O2− attracts the left two holes on sided d9 shells of the sided Cu atoms with their high energy, this increases the energy in the CuO plane, then CuO system reacted and decreases energy from 8J to 7 J by holes pairing through super exchange interaction between the two holes on each sides of O2−.This model is based on experimental and theoretical studies- SC in YBCO is hole type( Hall effect studies ); 2- holes after O doping accumulated around O2 – proved by various spectroscopic methods. 3- Theoretically proved that hole pairing decreases energy from 8J to 7 J.
