under the pressure of 1.5 atom., then the sealed Ta tubes were vacuum sealed into quartz tubes. The samples were put in box furnace and heated to 1170 $^{0}$C slowly and held there for a few hours before the temperature was decreased very slowly. The grown crystals have the form of platelets with shiny facets. The dimensions of the crystals are not so large as 122 crystals. The maximum size of the grown and mechanically cleaved samples are ∼ 5 × 5 × 0.2 mm $^{3}$. Their electronic and magnetic properties were measured on a Quantum Design physical property measurement system (PPMS) with the VSM option provided. 

Figure 1(a) shows the temperature dependence of resistivity for NaFe 0 . 95 Co 0 . 05 As crys- tal between 2.2 K and 300 K. No other anomalies are observed except for the supercon- ducting transition at 19 K (Here Tc is defined as the temperature where zero resistivity is achieved), which means no transitions related to magnetic or structural orders exist as found in Na 1 − δ FeAs single crystals.[20] The result is consistent with previous reports on Co doped NaFeAs polycrystalline samples,[24] where the magnetic and structural transitions are absent when the carriers like Co or Ni are introduced into the system and the bulk superconductivity is established. The inset of Fig. 1(a) shows the temperature dependence of the magnetization in the single crystal of NaFe 0 . 95 Co 0 . 05 As under the conditions of zero field cooling (ZFC) and field cooling (FC) at H=10 Oe. The perfect diamagnetism indicates the bulk superconductivity. Taking into account the Tcs in other Co doped system like 22 K in BaFe 2 − x Co x As 2 , 20 K in SrFe 2 − x Co x As 2 , 18-19 K in CaFe 2 − x Co x As 2 and 10-24 K in LnFe 1 − x Co x AsO (Ln=La, Ce, Nd, Sm etc. ), the transition temperature of 19 K is at the same level and consistent with previous reports on polycrystalline Co-doped NaFeAs.[24] Later in this paper we find P-doped NaFeAs presents much higher Tc compared with above values and it is even higher than all the Tcs realized through Co or P doping in their parent compounds in 122 or 1111 system. 

Figure1 (b) and (c) show the behavior of resistivity of NaFe 0 . 95 Co 0 . 05 As in external mag- netic field up to 14 T. In Fig. 1(b), the applied field is within the ab plane ( H ‖ ab ) while in Fig. 1(c) the applied field is parallel to the c axis ( H ‖ c ). We see the superconducting tran- sition is suppressed in both conditions but the effect of magnetic field is much larger when the field is applied along the c axis of the single crystals in stead of within the ab plane. The corresponding upper critical field H c 2 as a function of temperature obtained from a determi- nation of the midpoint of the resistive transition is plotted in Fig. 1(d). The curves are steep with slopes − dH c 2 /dT | T$_{c}$ =4.7 T/K for H ‖ ab and − dH c 2 /dT | T$_{c}$ =2.4 T/K for H ‖ c . According 

