Physica C 470 (2010) S309–S310
Physica C
Superconductivity of the ‘‘1 1 1” type iron pnictide LiFeP
*
Z. Deng, X.C. Wang, Q.Q. Liu, S.J. Zhang, Y.X. Lv, J.L. Zhu, R.C. Yu, C.Q. Jin
Institute of Physics, Chinese Academy of Science, Beijing 100080, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Accepted 16 November 2009
Available online 22 December 2009
We report studies on a new iron based LiFeP superconductor. The compound takes the same structure to
LiFeAs containing a ‘‘FeP” conduction layer. Superconductivity was achieved up to 6 K. The new supercon-
ductor is featured with itinerant behavior at normal state.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
LiFeP
Iron pnictide superconductor
‘‘1 1 1” type
1. Introduction
at 800 °C for 30 h. All preparative manipulations were carried out
in a glove box protected with high purity Ar.
After the discovery of the new superconductor LaFeAsO [1] of
the iron based superconductor, the superconductive transition
temperature Tc was optimized to 55 K by substituting other rare-
earth ions for La3+ and FÀ for O2À. Without changing the basic
structural unit, the iron pnictide layer, some new systems have
also been found to be superconductors, which are AEFe2As2 (AE
for alkali earth metal) [2] (1 2 2), AFeAs (A for alkali metal)
(1 1 1) [3], and FeSe (1 1) [4]. The high transition temperature in
these itinerant systems containing magnetic element Fe challenge
the conventional BCS theory [1–8]. It is very important to discover
the underlying superconducting mechanism for iron based super-
conductors. It will be helpful to quest the novel physics through
searching for new superconductors with simple crystal structure.
Here, we report a new superconductor LiFeP produced by com-
pletely substituting P for As in ‘‘1 1 1” system, which can become
superconductive with Tc up to 6 K.
The samples are characterized by X-ray powder diffraction with
a Philips X’pert diffractometer. The resistance was measured using
the standard four probe method with a PPMS system, while the DC
magnetic susceptibility was measured using SQUID magnetometer
(Quantum design).
3. Results and discussion
The ‘‘1 1 1” type LiFeP, the same as LiFeAs [3], crystallizes into
Cu2Sb type tetragonal layered structure with space group P4/
nmm [6], which is shown in Fig. 1. The lattice parameters obtained
for LiFeP are a = 3.692 Å, c = 6.031 Å. In comparison with LiFeAs,
LiFeP can be viewed as a compressed ‘‘1 1 1” phase. Moreover,
hydrostatic pressure made Tc of LiFeAs decreases linearly with
pressure at a rate of ꢀ1.38 K/GPa [7]. This can explain the lower
Tc of LiFeP.
2. Experimental
Fig. 2 shows the temperature dependence of the electric con-
ductivity of LiFeP. The normal state of LiFeP shows good metallic
behavior without an abrupt change of resistivity that usually pro-
ceeds the spin density wave (SDW) as manifested for the ‘‘1 1 1 1”
[5] or ‘‘1 2 2” [4] type iron based system. With the different nom-
inal composition of Li content, samples show almost the same
superconducting transition with Tocnset about 6 K. This is quite sim-
ilar to the LiFeAs, where the Tc seems not sensitive to the nominal
Li content [3]. The first-principle calculations for LiFeAs indicated
little change of density of states (DOS) or Fermi surface topology
with Li content that could account for its small influence on Tc
[8]. The same situation may be valid for the LiFeP case.
The polycrystalline samples of nominal LiFeP were synthesized
by conventional solid-state reaction. The starting materials of Li
and FeP are mixed according to the nominal formula. The FeP pre-
cursors were synthesized from high-purity Fe and P powders that
were sealed into an evacuated quartz tube and sintered at 800 °C
for 10 h. The compounds can be synthesized using either high pres-
sure method or traditional method. The former is sintering the
mixed materials wrapped with gold foil at 1.8 GPa, 800 °C for 1 h,
and the later is sintering the components sealed into a quartz tube
Fig. 3 shows the DC magnetic susceptibility for samples of LiFeP,
which are measured in both zero field cooling (ZFC) and field cool-
* Corresponding author. Tel.: +86 10 82649163; fax: +86 10 82649531.
0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
Deng
